Method for integrating biological tissues with a vascular system

ABSTRACT

The present invention provides a method of constituting a tissue construct in vitro using a tissue without depending on scaffold materials. 
     A method of integrating a biological tissue with a vascular system in vitro, comprising coculturing a biological tissue with vascular cells and mesenchymal cells. A biological tissue which has been integrated with a vascular system by the above-described method. A method of preparing a tissue or an organ, comprising transplanting the biological tissue described above into a non-human animal and differentiating the biological tissue into a tissue or an organ in which vascular networks have been constructed. A method of regeneration or function recovery of a tissue or an organ, comprising transplanting the biological tissue described above into a human or a non-human animal and differentiating the biological tissue into a tissue or an organ in which vascular networks have been constructed. A method of preparing a non-human chimeric animal, comprising transplanting the biological tissue described above into a non-human animal and differentiating the biological tissue into a tissue or organ in which vascular networks have been constructed. A method of evaluating a drug, comprising using at least one member selected from the group consisting of the biological tissue described above, the tissue or organ prepared by the method described above, and the non-human chimeric animal prepared by the method described above. A composition for regenerative medicine, comprising a biological tissue which has been integrated with a vascular system by the method described above.

TECHNICAL FIELD

The present invention relates to a method of biological tissues with avascular system. More specifically, the present invention relates to amethod of preparing three-dimensional tissues with vascular networksfrom tissues induced from pluripotent stem cells, etc. or tissues (suchas normal or cancer tissue) isolated from individuals.

BACKGROUND ART

Recently, the use of normal/cancer tissues isolated from individuals ortissues induced from pluripotent stem cells has attracted a great dealof attention as a way to realize drug discovery screening to develop newpharmaceuticals, and regenerative medicine to compensate for thefunctions of lost organs.

As attempts to induce three-dimensional tissues from pluripotent stemcells or the like, studies have been reported in which spheroidal tissuefragments are formed and directed for cell differentiation in such areasas the liver, pancreas or nerve (Non-Patent Document No. 1: Takayama K,et al., Biomaterials. 2013 February; 34(7):1781-9; Non-Patent DocumentNo. 2: Saito H, et al., PLoS ONE. 2011; 6(12): e28209; and Non-PatentDocument No. 3: Eiraku M, et al., Nature 2011, 472, 51-56). However,none of the tissues induced by those methods have vasculatures.Vasculatures have such a role that, once transplanted, they supply thetissues with oxygen and nutrients that are necessary for their survival.What is more, it is believed that, even before blood flows into thetissue, recapitulating three-dimensional tissue structures with bloodvessels and cell polarity as well is important for the differentiation,proliferation and maintenance of cells. Therefore, avascular tissues notonly fail to engraft upon transplantation and suffer from innernecrosis, but also fail to achieve tissue maturation that is associatedwith vascularization. It has, therefore, been difficult for avasculartissues to exhibit adequate functions.

Accordingly, for the purpose of integrating vasculatures to athree-dimensional tissue, a method has been invented in which tissues(such as pancreatic islets) isolated from individuals are seeded on acarrier (scaffold material) and cocultured with vascular endothelialcells, fibroblast cells, or the like (Non-Patent Document No. 4:Kaufman-Francis K, et al., PLoS ONE 2012, 7(7): e40741).

However, this method has a limitation in spatial arrangement caused byscaffold materials and cell behavior is greatly affected. Therefore, itis difficult for this method to construct a precise structure like abiological tissue and appropriate interactions between cells are notrecapitulated. Consequently, problems arise such as inhibited maturationand proliferation of cells in tissues, and delayed reconstitution offunctional vascular networks that leads to poor engraftment aftertransplantation. There is yet another serious problem that may occur intransplantation and the like; the scaffold material used causes aforeign-body reaction which will result in inflammation or the like.

As described above, reconstitution of three-dimensional tissues havingvascular networks is desirable if applications in industry andregenerative medicine are intended but, in fact, no method is yet to beestablished that is capable of constituting a tissue construct withvasculatures in vitro using a tissue without depending on scaffoldmaterials.

PRIOR ART LITERATURE Non-Patent Documents

-   Non-Patent Document No. 1: Takayama K, et al., Biomaterials. 2013    February; 34(7):1781-9-   Non-Patent Document No. 2: Saito H, et al., PLoS ONE. 2011; 6(12):    e28209-   Non-Patent Document No. 3: Eiraku M, et al., Nature 2011, 472, 51-56-   Non-Patent Document No. 4: Kaufman-Francis K, et al., PLoS ONE 2012,    7(7): e40741

DISCLOSURE OF THE INVENTION Problem for Solution by the Invention

For the realization of drug development and regenerative medicine fordiseases in the liver, pancreas, kidney, intestine, lung, etc., it isessential to recapitulate a three-dimensional tissue structureassociated with vascularization, as well as cell polarity. Briefly, inorder to maximize the function of a tissue induced from pluripotent stemcells or a tissue isolated from an individual, it is necessary to form athree-dimensional tissue construct that enables reconstitution ofvascular networks.

In this connection, the present inventors have established an innovativethree-dimensional culture technique which realized “directeddifferentiation of organ cells based on organ reconstitution”, byutilizing spatiotemporal interactions between different cell lineages(Nature, 499:481-484, 2013; WO2013/047639 titled “Method for ProducingTissue and Organ”). Briefly, by recapitulating those intracellularinteractions among organ cells, vascular cells and mesenchymal cellswhich are essential for early processes of organogenesis, a primordiumof steric organ (an organ bud) is induced, thus providing a platform forenabling the generation of functional organs with vascular networks.However, this method starts with organ cells and it has not beenelucidated as to whether a primordium of three-dimensional tissue withvascular networks can be generated by using a tissue fragment(tissue).

The present invention aims at providing a method of constituting atissue construct with vasculatures in vitro from a tissue withoutdepending on scaffold materials.

Means to Solve the Problem

The present inventors have found that close intercellular reactionsbetween organ cells (from which organs develop) and vascular endothelialcells/mesenchymal cells direct the progress of steric tissue formationthat involves autonomous tissue structure constitution and celldifferentiation (Nature, 499:481-484, 2013; WO2013/047639 titled “Methodfor Producing Tissue and Organ”). However, it is yet to be made clear ifvascular networks can be integrated into tissue fragments.

The present invention attempts to artificially generate steric tissueshaving vascular networks in vitro starting with tissues by artificiallyrecapitulating such early processes of organogenesis. Further, bytransplanting the steric tissues into living bodies, the presentinvention intends to create a vascularized steric tissue which, whentransplanted into a living body after being induced in a culture system,restarts blood flow to enable the tissue function to achieve maturationand maintenance.

The present inventors have cocultured tissues isolated from individuals(up to approximately 10-3,000 μm) or tissues induced from pluripotentstem cells (up to approximately 10-3,000 μm) with vascular cells andmesenchymal cells at appropriate mixing ratios. The methods describedbelow were used for inducing steric tissues.

1. Three-dimensional tissues are formed by coculturing tissues withvascular/mesenchymal cells on a carrier such as Matrigel.2. Three-dimensional tissues are formed by coculturing tissues withvascular/mesenchymal cells on a plate of such a shape that cells gatherin the bottom.

By culturing tissues for a short period according to the above-describedmethods, it was possible to induce in vitro steric tissues integratedwith microvasculatures.

Further, the present inventors successfully created tissues/organs witha highly ordered tissue structure comparable to that of adult tissues;when the steric tissues induced in a culture system were by transplantedinto living bodies, reconstruction of functional vascular networks wasinduced, whereupon blood perfusion was restarted to create theabove-described tissues/organs.

This technique of attempting three-dimensional reconstitution oftissues/organs based on the induction of self-organization from tissuesthrough intercellular interactions was not available in the past and isbelieved to provide a method whose novelty is extremely high.

A summary of the present invention is as described below.

-   (1) A method of integrating a biological tissue with a vascular    system in vitro, comprising coculturing a biological tissue with    vascular cells and mesenchymal cells.-   (2) The method of (1) above, wherein the biological tissue is    cocultured with vascular cells and mesenchymal cells without using    scaffold materials.-   (3) The method of (1) or (2) above, wherein by coculturing the    biological tissue with vascular cells and mesenchymal cells, the    biological tissue is integrated with a vascular system so that the    function of the biological tissue is maintained and/or improved.-   (4) A biological tissue which has been integrated with a vascular    system by the method of any one of (1) to (3) above.-   (5) A method of preparing a tissue or an organ, comprising    transplanting the biological tissue of (4) above into a non-human    animal and differentiating the biological tissue into a tissue or an    organ in which vascular networks have been constructed.-   (6) A method of regeneration or function recovery of a tissue or an    organ, comprising transplanting the biological tissue of (4) above    into a human or a non-human animal and differentiating the    biological tissue into a tissue or an organ in which vascular    networks have been constructed.-   (7) A method of preparing a non-human chimeric animal, comprising    transplanting the biological tissue of (4) above into a non-human    animal and differentiating the biological tissue into a tissue or    organ in which vascular networks have been constructed.-   (8) A method of evaluating a drug, comprising using at least one    member selected from the group consisting of the biological tissue    of (4) above, the tissue or organ prepared by the method of (5)    above, and the non-human chimeric animal prepared by the method    of (7) above.-   (9) A composition for regenerative medicine, comprising the    biological tissue of (4) above.-   (10) The composition of (9) above, which is used for preparing a    tissue or an organ.-   (11) The composition of (9) above, which is used for regeneration or    function recovery of a tissue or an organ.-   (12) The composition of any one of (9) to (11) above, wherein the    biological tissue differentiates into a tissue or an organ with    vascular networks upon transplantation into a living body.

According to the present invention, normal/cancer tissues isolated fromindividuals or tissues induced from pluripotent stem cells arecocultured with vascular cells and mesenchymal cells under appropriateenvironments, whereby it has become possible to constitute steric tissueconstructs in vitro that are integrated with vascular networks. Sincevascular networks which are essential for maturation, maintenance,repair, etc. of tissues are provided, highly functional tissues arereconstituted, potentially providing a platform for preparing tissueconstructs useful for drug discovery screening and regenerativemedicine.

Conventionally, tissue constructs obtained from pluripotent stem cellsby directed differentiation remained less mature in the differentiationstage than functional cells that constitute adult tissues. This isbecause terminal differentiation of functional cells has not beenachieved by the conventional directed differentiation method.

According to the present invention, it has become possible toreconstitute a tissue integrated with vascular networks and one mayexpect that a method of directing terminal differentiation of humanfunctional cells will be established (for example, reconstitution ofcell polarity in vasculature); hence, the present invention is highlyvaluable as a technique for creating human functional cells.

On the other hand, the tissues derived from organs removed fromindividuals markedly deteriorate in function immediately after they areisolated and it has been difficult to maintain their functions. If animprovement/maintenance of a tissue's function is achieved byintegrating vascular networks to it according to the present invention,it may be possible to provide a transplantation technique withremarkable therapeutic efficacy for those patients who have notbenefited adequately from the conventional tissue transplantationtherapies for the reason that the transplant has no vascular system(e.g., islet transplantation therapy). Further, it will become possibleto maximize the functions of various organs in vitro or in vivo and onemay expect that the present invention will provide a platform useful fordrug discovery screening.

Further, according to the present invention, it is possible toreconstitute a steric human tissue construct having a vascular system.Therefore, it will become possible to generate a tissue or an organ thatpermits a blood flow in an appropriately arranged vascular system andwhich has been entirely unachievable by conventional techniques.Consequently, one may expect that the present invention will provide acompletely novel analysis system for evaluating the efficacy ofpharmaceuticals by which the relationship between development of drugefficacy and blood vessels and other factors that have been difficult toanalyze by existing evaluation systems can be evaluated.

Further, the advantages the present invention have over the previouslydisclosed method (Nature, 499:481-484, 2013; WO2013/047639) in whichclose intercellular reactions between organ cells and vascularendothelial cells/mesenchymal cells are relied upon to direct theprogress of steric tissue formation that involves autonomous tissuestructure constitution and cell differentiation may be enumerated asfollows.

1. It is possible to provide a vascular system even for those tissueswhich are constituted from difficult-to-expand cells (such as pancreaticβ cells, renal glomerular epithelial/renal tubular epithelial cells,hepatic cells, intestinal epithelial cells, alveolar epithelial cells,tumor cells, trophectodermal cells, iPS cell-derived endodermal cells,iPS cell-derived mesodermal cells, iPS cell-derived from ectodermalcells and iPS cell-derived tissue stem/progenitor cells) and examples ofsuch tissues include pancreatic islets, renal glomeruli, liver tissues,intestinal crypts, pulmonary alveoli, tumor tissues, trophectodermaltissues, iPS cell-derived endodermal cell-derived spheroids, iPScell-derived mesodemial cell-derived spheroids, iPS cells-derivedectodermal cell-derived spheroids and iPS cell-derived tissuestem/progenitor cell-derived spheroids.2. It is possible to provide a vascular system for larger tissues.Tissues can be generated by the method disclosed in Nature, 499:481-484,2013; WO2013/047639 only in the case where isolated cells are used. Themethod of the present invention has been confirmed to be capable ofintegrating a vascular system for tissues, rather than cells, that areapproximately 10-3,000 μm in size.3. By integrating a vascular system for a tissue fragment derived fromstem cells such as iPS cells, it is possible to recapitulateenvironments which are similar to the developmental processes ofbiological tissues and directed differentiation into functional cellsthat constitute a tissue of interest can be achieved efficiently.

Effect of the Invention

According to the present invention, normal or cancer tissues isolatedfrom individuals or tissues induced from pluripotent stem cells or thelike are cocultured with vascular cells and mesenchymal cells, wherebyit has become possible to constitute steric tissue constructs in vitrothat are integrated with vascular networks. This technique is applicableto, for example, generation of human functional cells; organtransplantation; drug discovery screening; novel analysis systems toevaluate the relationship between development of drug efficacy and bloodvessels.

The present specification encompasses the contents disclosed in thespecification and/or drawings of Japanese Patent Application No.2013-153056 based on which the present application claims priority.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A This figure shows the integration of vascular networks topancreatic islet (hereinafter, frequently referred to simply as “islet”)tissues.

A) Validation of media for culturing mouse islets using Live/Dead™ CellImaging Kit (green: viable cells, red: dead cells).

FIG. 1B This figure shows the integration of vascular networks to islettissues.

B) Quantification data for A).

FIG. 1C This figure shows the integration of vascular networks to islettissues.

C) Time-lapse imaging of three-dimensional tissue constituting processesusing mouse islets (colorless), vascular endothelial cells (green) andmesenchymal stem cells (red).

FIG. 1DE This figure shows the integration of vascular networks to islettissues.

D) Mouse islets at 24 hours of culture.E) Mouse islets, vascular endothelial cells and mesenchymal stem cellsat 24 hours of coculture.E′) Immunohistological analysis of the three-dimensional tissuegenerated in E) (green: insulin, red: human CD31).

FIG. 1F This figure shows the integration of vascular networks to islettissues.

F) Determination of survival or death of mouse islet cells usingLive/Dead™ Cell Imaging Kit (green: viable cells, red: dead cells).

FIG. 1G This figure shows the integration of vascular networks to islettissues.

G) Quantification data for F).

FIG. 1H This figure shows the integration of vascular networks to islettissues.

H) Increase of insulin concentration released from cocultured mouseislets.

FIG. 1I This figure shows the integration of vascular networks to islettissues.

I) Glucose tolerance test in vitro.

FIG. 1J-1 This figure shows the integration of vascular networks toislet tissues.

J-1) Group of genes whose expressions are markedly enhanced by coculturewith vascular endothelial cells and mesenchymal stem cells.

FIG. 1J-2 This figure shows the integration of vascular networks toislet tissues.

J-2) Continuation from J-1).

FIG. 1J-3 This figure shows the integration of vascular networks toislet tissues.

J-3) Continuation from J-2).

FIG. 2A This figure shows preparation of vascularized islet fragments.

A) Autonomous formation of vascularized islet fragments using a cultureplate of such a shape that cells gather in the bottom (vascularizedtissues are formed even when the number of mouse islets is changed).

FIG. 2B This figure shows preparation of vascularized islet fragments.

B) Reviewing the conditions of vascular endothelial cell number andmesenchymal stem cell number.

FIG. 2C This figure shows preparation of vascularized islet fragments.

C) Time-lapse imaging of the processes of formation of vascularizedislet fragments (changes in cell morphology caused by coculture; mouseislets: blue; vascular endothelial cells: green; mesenchymal stem cells:red).

FIG. 2D This figure shows preparation of vascularized islet fragments.

D) Prepared vascularized islet fragments; mouse islets (red), vascularendothelial cells (green) and mesenchymal stem cells (colorless).

FIG. 2E This figure shows preparation of vascularized islet fragments.

E) Histological analysis of vascularized islet fragments; mouse islets(red), vascular endothelial cells (green), mesenchymal stem cells(colorless) and mouse CD31 (blue).

FIG. 3AB This figure shows validation of function upon transplantationof vascularized tissue.

A) Macroimaging of the site of transplantation of vascularized islets(yellow arrow indicates blood inflow).B) Macroimaging of the site of transplantation of islets alone (controlgroup).

FIG. 3CD This figure shows validation of function upon transplantationof vascularized tissue.

C) Blood perfusion into vascularized islets; mouse islets (green),vascular endothelial cells (colorless), mesenchymal stem cells(colorless), dextran (red).D) Blood perfusion around transplanted islets; mouse islets (green),vascular endothelial cells (colorless), mesenchymal stem cells(colorless), dextran (red).

FIG. 3E This figure shows validation of function upon transplantation ofvascularized tissue.

E) Transplantation of vascularized islets into the subcapsular space ofthe kidney using diabetes model mice; blood glucose transition.

FIG. 3F This figure shows validation of function upon transplantation ofvascularized tissue.

F) Blood glucose transition in diabetes model mice.

FIG. 3G This figure shows validation of function upon transplantation ofvascularized tissue.

G) Body weight transition in diabetes model mice.

FIG. 3H This figure shows validation of function upon transplantation ofvascularized tissue.

H) Survival ratios in diabetes model mice.

FIG. 3I This figure shows validation of function upon transplantation ofvascularized tissue.

I) In vivo glucose tolerance test.

FIG. 3JK This figure shows validation of function upon transplantationof vascularized tissue.

J) Histological analysis of vascularized islets transplanted into CW.K) Histological analysis of islets transplanted into CW.

FIG. 3L This figure shows validation of function upon transplantation ofvascularized tissue.

L) Histological analysis of vascularized islets transplanted into thesubcapsular space of the kidney; insulin (green), laminin (red), DAPI(blue).

FIG. 3M This figure shows validation of function upon transplantation ofvascularized tissue.

M) Histological analysis of islets transplanted into the subcapsularspace of the kidney; insulin (green), laminin (red), DAPI (blue).

FIG. 4 This figure shows the integration of vascular networks to renalglomeruli.

A) Autonomous formation of a three-dimensional tissue derived from mouserenal glomeruli, vascular endothelial cells and mesenchymal stem cellsusing a 24-well dish.B) Autonomous formation of a three-dimensional tissue derived from mouserenal glomeruli, vascular endothelial cells and mesenchymal stem cellsusing a culture plate (substrate?) of such a shape that cells gather inthe bottom (time-lapse imaging of the three-dimensional tissue usingmouse renal glomeruli (green), vascular endothelial cells (red) andmesenchymal stem cells (blue)).C) Macroscopic image of vascularized three-dimensional mouse renalglomerular tissue at 24 hours of culture using a 24-well dish.D) Macroscopic image of vascularized three-dimensional mouse renalglomerular tissue at 24 hours of culture using a 96-well dish.E) Confirmation of vascularization and engraftment at the site oftransplantation of vascularized renal glomeruli.F) Live imaging of the site of transplantation of vascularized renalglomeruli (mouse renal glomeruli (red), human vascular endothelial cells(green), mouse vascular endothelial cells (blue)).

FIG. 5 This figure shows the integration of vascular networks to tumortissues.

A) Autonomous formation of a three-dimensional tissue derived from humanpancreatic tumor tissue (red), vascular endothelial cells (green) andmesenchymal stem cells (colorless) using a 24-well dish.B) Lapse imaging of a three-dimensional tissue formed autonomously frommouse pancreatic cancer tissue, vascular endothelial cells andmesenchymal stem cells at 24 hours of culture using a 24-well dish.C) Enhanced expression of a cancer stem cell marker (CD44) by formationof vascularized tissue.

FIG. 6 This figure shows the integration of vascular networks to livertissues.

A) Time-lapse imaging of the process of formation of a three-dimensionaltissue derived from mouse liver tissues (green), vascular endothelialcells (red) and mesenchymal stem cells (colorless).B) Autonomous formation of a three-dimensional tissue derived from mouseliver tissues (green), vascular endothelial cells (red) and mesenchymalstem cells (colorless) using a culture plate (substrate?) of such ashape that cells gather in the bottom.C) Macroimaging of the site of transplantation of vascularized livertissues.D) Reconstitution of a vascular system inside the vascularized livertissues.

FIG. 7 This figure shows the integration of vascular networks tointestinal tissues.

A) Time-lapse imaging of the process of formation of a three-dimensionaltissue using mouse intestinal tissues (red), vascular endothelial cells(green) and mesenchymal stem cells (colorless).B) Autonomous formation of a three-dimensional tissue derived fromintestinal tissues (red), vascular endothelial cells (green) andmesenchymal stem cells (colorless) using a culture plate (substrate?) ofsuch a shape that cells gather in the bottom.C) Macroimaging of the site of transplantation of vascularizedintestinal tissues.D) In vivo live imaging of the site of transplantation of vascularizedintestinal tissues (mouse intestinal tissues (red), vascular endothelialcells (green) and mesenchymal stem cells (colorless)).

FIG. 8 This figure shows the integration of vascular networks topulmonary tissues.

A) Autonomous formation of a three-dimensional tissue using mousepulmonary tissues (red), vascular endothelial cells (green) andmesenchymal stem cells (colorless).B) Macroimaging of the site of transplantation of vascularized pulmonarytissue.C) In vivo live imaging of the site of transplantation of vascularizedpulmonary tissue (mouse pulmonary tissues (red), vascular endothelialcells (green), mesenchymal stem cells (colorless) and mouse CD31(blue)).

FIG. 9 This figure shows the integration of vascular networks to iPScell-derived endodermal tissues.

A) Outline of the method of application to human iPS cell-derivedendodermal cell spheroids.B) Autonomous formation of a three-dimensional tissue using human iPScell-derived endodermal tissue fragments, vascular endothelial cells andmesenchymal stem cells.C) Fluorescent image observation of a three-dimensional tissueconstituted from human iPS cell-derived endodermal tissue fragments(colorless), vascular endothelial cells (red) and mesenchymal stem cells(colorless).

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be described in detail.

The present invention provides a method of integrating a vascular systemfor a biological tissue in vitro, comprising coculturing a biologicaltissue with vascular cells and mesenchymal cells.

In the present specification, the term “biological tissue” refers to aconstruct constituted from a plurality of cells. For example,normal/abnormal tissues or cancer tissues isolated from individuals aswell as tissues induced from pluripotent stem cells (such as inducedpluripotent stem cells (iPS cells) and embryonic stem cells (ES cells)),tissue stem/progenitor cells, differentiated cells or the like may beenumerated. As biological tissues, those derived from humans mayprimarily be used. Biological tissues derived from non-human animals(e.g., animals used, for example, as experimental animals, pet animals,working animals, race horses or fighting dogs; more specifically, mouse,rat, rabbit, pig, dog, monkey, cattle, horse, sheep, chicken, shark,devilfish, ratfish, salmon, shrimp, crab or the like) may also be used.

In the present specification, the term “vascular system” refers to astructure composed of vascular endothelial cells and its supportingcells. Vascular systems not only mainain tissues but also play animportant role in the maturation process of tissues. Vascular structureshave such a role that, once transplanted, they supply the tissues withoxygen and nutrients that are necessary for their survival. What ismore, it is believed that even before blood flows into the tissue,recapitulating three-dimensional tissue structures with blood vesselsand cell polarity as well is important for the differentiation,proliferation and maintenance of cells. Therefore, avascular tissues notonly fail to engraft upon transplantation and suffer from innernecrosis, but also fail to achieve tissue maturation that is associatedwith vascularization. It has, therefore, been difficult for avasculartissues to exhibit adequate functions.

In the present specification, the terms “integrating a vasculaturesystem” and “vascularization” mean that a vascular system composed ofvascular endothelial cells and its supporting cells is integrateddirectly with a target tissue. When a biological tissue integrated witha vascular system is transplanted into a living body, maturation ofblood vessels is observed and upon connecting to the host blood vessels,blood perfusion starts, enabling induction to a functional tissue/organhaving vascular networks.

Vascular cells may be isolated from vascular tissues but they are in noway limited to those isolated therefrom. Vascular cells may be derivedfrom totipotent or pluripotent cells (such as iPS cells and ES cells) byinduction of differentiation. As vascular cells, vascular endothelialcells are preferable. In the present specification, the term “vascularendothelial cells” means cells constituting vascular endothelium orcells capable of differentiating into such cells (for example, vascularendothelial progenitor cells and vascular endothelial stem cells).Whether a cell is vascular endothelial cell or not can be determined bychecking to see if they express marker proteins such as TIE2, VEGFR-1,VEGFR-2, VEGFR-3 and CD31 (if any one or more of the above-listed markerproteins are expressed, the cell can safely be regarded as a vascularendothelial cell). Further, as markers for vascular endothelialprogenitor cells, c-kit, Sca-1, etc. have been reported. If thesemarkers are expressed, the cell of interest can be confirmed as avascular endothelial progenitor cell (S. Fang, et al., PLOS Biology,2012; 10(10): e1001407). Among the terms used by those skilled in theart, the following are included in the “vascular endothelial cell” ofthe present invention: endothelial cells, umbilical vein endothelialcells, endothelial progenitor cells, endothelial precursor cells,vasculogenic progenitors, hemangioblast (H J. Joo, et al. Blood. 25;118(8):2094-104 (2011)) and so on. As vascular cells, human-derivedcells are mainly used. However, vascular cells derived from non-humananimals (e.g., animals used, for example, as experimental animals, petanimals, working animals, race horses or fighting dogs; morespecifically, mouse, rat, rabbit, pig, dog, monkey, cattle, horse,sheep, chicken, shark, devilfish, ratfish, salmon, shrimp, crab or thelike) may also be used. Vascular cells may be obtained from cord blood,umbilical cord vessels, neonatal tissues, liver, aorta, brain, bonemarrow, adipose tissues, and so forth.

In the present invention, the term “mesenchymal cells” means connectivetissue cells that are mainly located in mesodemi-derived connectivetissues and which form support structures for cells that function intissues. The “mesenchymal cell” is a concept that encompasses thosecells which are destined to, but are yet to, differentiate intomesenchymal cells. Mesenchymal cells to be used in the present inventionmay be either differentiated or undifferentiated. Preferably,undifferentiated mesenchymal cells are used. Whether a cell is anundifferentiated mesenchymal cell or not may be confirmed by checking tosee if the cell expresses marker proteins such as Stro-1, CD29, CD44,CD73, CD90, CD105, CD133, CD271 or Nestin (if any one or more of theabove-listed marker proteins are expressed, the cell can safely beregarded as an undifferentiated mesenchymal cell). A mesenchymal cell inwhich none of the above-listed markers is expressed can be judged asdifferentiated mesenchymal cell. Among the terms used by those skilledin the art, the following are included in the “mesenchymal cell” of thepresent invention: mesenchymal stem cells, mesenchymal progenitor cells,mesenchymal cells (R. Peters, et al. PLoS One. 30; 5(12):e15689 (2010))and so on. As mesenchymal cells, human-derived cells are mainly used.However, mesenchymal cells derived from non-human animals (e.g., animalsused, for example, as experimental animals, pet animals, workinganimals, race horses or fighting dogs; more specifically, mouse, rat,rabbit, pig, dog, monkey, cattle, horse, sheep, chicken, shark,devilfish, ratfish, salmon, shrimp, crab or the like) may also be used.

The size of a biological tissue to be cocultured with vascular cells andmesenchymal cells may be approximately 10-500 μm, but is not limited tothis range. Preferably, the size is approximately 100-300 μm. Morepreferably, the size is approximately 100-150 μm.

The numbers of vascular cells and mesenchymal cells to be used forcoculture may each be about 2×10²-1×10⁵ cells, preferably, about2×10²-5×10⁴ cells, and more preferably, about 1×10⁴ cells, perbiological tissue of approx. 150 μm in size.

The culture ratio of vascular cells and mesenchymal cells in cocultureis not particularly limited if it is within such a range that a vascularsystem is provided for biological tissues. A preferable cell count ratioas expressed by the vascular cell to mesenchymal cell is 10-3:3-1.

The number of biological tissues in coculture is not particularlylimited if it is within such a range that a vascular system is providedfor biological tissues. Preferably, 1-100 tissues approx. 100-150 μm indiameter are used for a mixture of 1×10⁴ vascular cells and 1×10⁴mesenchymal cells.

Either one or both of vascular cells and mesenchymal cells may besubstituted by substances such as factors secreted by vascular cells,factors secreted by mesenchymal cells, and factors secreted as a resultof the presence of both vascular cells and mesenchymal cells.

Examples of the substances such as factors secreted by vascular cells,factors secreted by mesenchymal cells, and factors secreted as a resultof the presence of both vascular cells and mesenchymal cells include,but are not limited to, FGF2, FGF5, BMF4, BMP6, CTGF, angiopoietin 2,chemokine (C-C motif) ligand 14 and von Willebrand factor.

With respect to the amount of addition of these substances, FGF2 may beadded at 10-100 ng/ml, preferably at about 20 ng/ml, per 1×10⁶ cells;and BMF4 may be added at 10-100 ng/ml, preferably at about 20 ng/ml, per1×10⁶ cells.

The medium used for culturing is not particularly limited. Any mediummay be used as long as it enables the integration of a vascular systemfor biological tissues. Preferably, a medium for culturing vascularcells (in particular, vascular endothelial cells), a medium forculturing biological tissues or a mixture of these two media may beused. As a medium for culturing vascular cells (in particular, vascularendothelial cells), any medium may be used but, preferably, a mediumcontaining at least one of the following substances may be used: hEGF(recombinant human epithelial growth factor), VEGF (vascular endothelialgrowth factor), hydrocortisone, bFGF, ascorbic acid, IGF1, FBS,antibiotics (e.g., gentamycin or amphotericin B), heparin, L-glutamine,phenol red and BBE. As a medium for culturing vascular endothelialcells, EGM-2 BulletKit (Lonza), EGM BulletKit (Lonza), VascuLife EnGSComp Kit (LCT), Human Endothelial-SFM Basal Growth Medium (Invitrogen),human microvascular endothelial cell growth medium (Toyobo) or the likemay be used. The medium used for culturing biological tissues is notparticularly limited but, as a medium for culturing islet tissues,RPMI1640 (Wako) or EGM™ BulletKit™ (Lonza CC-4133) supplemented with 10%fetal bovine serum (BWT Lot.S-1560), 20 mmol/L L-glutamine (Gibco) and100 μg/ml penicillin/streptomycin (Gibco) may preferably be used; as amedium for culturing renal tissues (such as renal glomeruli), RPMI1640(Wako) supplemented with 20% fetal bovine serum (BWT Lot.S-1560), 100μg/ml penicillin/streptomycin (Gibco) and Insulin-Transferrin-SeleniumX(Gibco) may preferably be used; as a medium for culturing intestinaltissues (such as crypt fragments), RPMI1640 (Wako) supplemented with 20%fetal bovine serum (BWT Lot.S-1560), 100 μg/ml penicillin/streptomycin(Gibco) and Insulin-Transferrin-SeleniumX (Gibco) may preferably beused; as a medium for culturing liver tissues, DMEM/F12 (Invitrogen)supplemented with 10% fetal bovine serum (ICN Lot.7219F), 2 mmol/LL-glutamine (Gibco), 100 μg/mL penicillin/streptomycin (Gibco), 10mmol/L nicotinamide (Sigma), 50 μmol/L 2-Mercaptoethanol, 1×10⁻⁷ mol/L6.5% dexamethasone (Sigma), 2.6×10⁻⁴ M L-Ascorbic acid 2-phosphatesesquimagnesium salt hydrate (Sigma), 5 mmol/L HEPES (Dojindo), 1 μg/mLHuman recombinant insulin expressed in yeast (Wako), 50 ng/mL Humanrecombinant HGF expressed in Sf21 insect cells (Sigma) and 20 ng/mLMouse Submaxillary Glands EGF (Sigma) may preferably be used; as amedium for iPS cell-derived endodermal tissues, RPMI1640 (Wako)supplemented with 1% B27 SUPPLEMENT X50 (Invitrogen 17504-044), 10 nG/MLBFGF Recombinant Human (Wako 060-04543) and 20 nG/ML BMP4 RecombinantHuman (R&D 314-BP) may preferably be used; as a medium for iPScell-derived hepatic endodermal tissues, a medium kit for sole use withhepatocytes (HCM™ BulletKit™ lonza CC3198) freed of hEGF (recombinanthuman epithelial growth factor) and supplemented with 0.1 μMDexamethasone (Sigma-Aldrich), 10 ng/ml Oncostatin M (R&D) and 10 ng/mlHGF (PromoKine) may preferably be used; and as a medium for cancertissues or pulmonary tissues, the same media as that for vascular cellsmay preferably be used.

Preferably, biological tissues are seeded on a substrate such as gel andcocultured with vascular cells and mesenchymal cells. The substrate maybe a base material having a stiffness of 0.5-25 kPa. Examples of suchbase material include, but are not limited to, gels (e.g., ranging froma stock solution to a 4-fold dilution of Matrigel™, agarose gel,acrylamide gel, hydrogel, collagen gel or urethane gel).

Alternatively, biological tissues may be cocultured with vascular cellsand mesenchymal cells on a plate of such a shape that cells gather inthe bottom. The plate used for this purpose is not particularly limitedas long as it has such a shape that cells gather in the bottom. Forexample, PrimeSurface™ 96-well U plate (Sumitomo Bakelite) may be used.

The temperature at the time of culture is not particularly limited butit is preferably 30-40° C., more preferably 37° C.

The time period of culture is not particularly limited but it ispreferably 12-144 hours. For vascularization of adult tissues such asislets, the culture period is more preferably about 12-24 hours. Forvascularization of iPS cell-derived tissues, the culture period is morepreferably about 48-72 hours. For vascularization of cancer tissues, theculture period is more preferably about 12-72 hours.

The biological tissue that has been integrated with a vascular system bythe method of the present invention may be a construct characterized inthat the complex tissue is autonomously formed by cells or tissues.Further, the biological tissue that has been integrated with a vascularsystem by the method of the present invention may be a complex tissue inwhich the vascular system directly integrates with (i.e., adheres to,connects to, or continues to) the tissue.

In the method of the present invention, it is possible to provide avascular system for a biological tissue by coculturing the biologicaltissue with vascular cells and mesenchymal cells without using scaffoldmaterials.

When a vascular system is provided for a biological tissue bycoculturing the biological tissue with vascular cells and mesenchymalcells, the function of the biological tissue can be maintained and/orimproved. In addition to the maintenance and improvement of the functionof the biological tissue, transplantation efficiency is sufficientlyimproved to provide a treatment method having remarkable therapeuticeffects.

Further, the present invention which enables reconstruction of avascular system will leads to the establishment of a method by whichterminally differentiated cells can be efficiently induced from tissuesderived from pluripotent stem cells such as iPS cells and ES cells.

The biological tissue that has been integrated with a vascular system bythe method of the present invention may be a complex tissue whosevascular system is capable of rapidly functioning in vivo. Briefly, whenthe biological tissue integrated with a vascular system by the method ofthe present invention is transplanted into a living body (host), thetime it takes for anastomosis to host vessels to occur and for blood toflow in can be greatly shortened, compared to cases where scaffoldmaterials are used [for example, when scaffold materials are used, 12days are taken (Engineered blood vessel networks connect to hostvasculature via wrapping-and-tapping anastomosis. Blood. 2011 Oct. 27;118(17):4740-9) whereas the method of the present invention takes only 1to 2 days (see Examples described later)].

When the biological tissue integrated with a vascular system by themethod of the present invention is transplanted into a non-human animal,vascular networks are constructed in the transplanted tissue and bloodperfusion starts to enable the creation of a tissue or an organ having ahighly ordered tissue structure. Therefore, the present inventionprovides a method of preparing a tissue or an organ, comprisingtransplanting a human or a non-human animal with a biological tissuethat has been integrated with a vascular system by coculturing withvascular cells and mesenchymal cells, and differentiating the biologicaltissue into a tissue or an organ in which vascular networks have beenconstructed. Non-human animals to be used in this method include, butare not limited to, animals used, for example, as experimental animals,pet animals, working animals, race horses or fighting dogs; morespecifically, mouse, rat, rabbit, pig, dog, monkey, cattle, horse,sheep, chicken, shark, devilfish, ratfish, salmon, shrimp, crab or thelike may be used. Further, in order to avoid immunorejection, thenon-human animal to be used herein is preferably an immunodeficientanimal.

The site of transplantation of the biological tissue integrated with avascular system may be any site as long as transplantation is possible.Specific examples of the transplantation site include, but are notlimited to, the intracranial space, the mesentery, the liver, thespleen, the kidney, the subcapsular space of the kidney, and thesupraportal space. When the biological tissue is to be transplanted intothe intracranial space, about 1 to 12 biological tissues of 500 μm insize, prepared in vitro, may be transplanted. When the biological tissueis to be transplanted into the mesentery, about 1 to 12 biologicaltissues of 3-8 mm in size, prepared in vitro, may be transplanted. Whenthe biological tissue is to be transplanted into the supraportal space,about 1 to 12 biological tissues of 3-8 mm in size, prepared in vitro,may be transplanted. When the biological tissue is to be transplantedinto the subcapsular space of the kidney, about 1 to 6 biologicaltissues of 3-8 mm in size, prepared in vitro, may be transplanted. Whenthe biological tissue is to be transplanted into the liver, spleen,kidney, lymph node or blood vessel, about 100-2000 biological tissues of100-200 μm in size, prepared in vitro, may be transplanted.

The tissues and organs prepared as described above may be used in drugdiscovery screening and regenerative medicine.

Thus, the present invention provides a method of regeneration orfunction recovery or a tissue or an organ, comprising transplanting ahuman or a non-human animal with a biological tissue that has beenintegrated with a vascular system by coculturing with vascular cells andmesenchymal cells into, and differentiating the biological tissue into atissue or an organ in which vascular networks have been constructed.Non-human animals to be used in this method include, but are not limitedto, animals used, for example, as experimental animals, pet animals,working animals, race horses or fighting dogs; more specifically, mouse,rat, rabbit, pig, dog, monkey, cattle, horse, sheep, chicken, shark,devilfish, ratfish, salmon, shrimp, crab or the like may be used.

Further, the present invention provides a composition for regenerativemedicine, comprising a biological tissue that has been integrated with avascular system by coculturing with vascular cells and mesenchymalcells.

The composition of the present invention can be transplanted into aliving body to prepare a tissue or an organ. The composition of thepresent invention can also be transplanted into a living body toregenerate a tissue or an organ or recover its function. As the livingbody, not only humans but also animals (such as ones used asexperimental animals, pet animals, working animals, race horses orfighting dogs; more specifically, mouse, rat, rabbit, pig, dog, monkey,cattle, horse, sheep, chicken, shark, devilfish, ratfish, salmon,shrimp, crab or the like) may be used.

After the composition of the present invention is transplanted into aliving body, the biological tissue is capable of differentiating into atissue or an organ having vascular networks. In the vascular networks,blood perfusion can occur. It is believed that the occurrence of bloodperfusion in the vascular networks enables generation of a tissue or anorgan having a highly ordered tissue structure either comparable ornearly comparable to the tissue structure of adult tissues.

The composition of the present invention may contain additivesincluding, for example, tissue vascularization promoters such as FGF2,HGF and VEGF; gelatin sponge for hemostasis associated withtransplantation (product name: Spongel; Astellas Pharma); and tissueadhesives used to fix transplanted tissues, such as Bolheal (TeijinPharma), Beriplast™ (CSL Behring) and TachoComb™ (CSL Behring).

The present invention also provides a method of preparing a non-humanchimeric animal, comprising transplanting a non-human animal with abiological tissue that has been integrated with a vascular system bycoculturing with vascular cells and mesenchymal cells, anddifferentiating the biological tissue into a tissue or an organ in whichvascular networks have been constructed. The non-human animal (such asmouse) transplanted with the biological tissue integrated with avascular system can mimic the physiological function of the animalspecies (such as human) from which the vascularized biological tissue isderived. Non-human animals include, but are not limited to, animalsused, for example, as experimental animals, pet animals, workinganimals, race horses or fighting dogs; more specifically, mouse, rat,rabbit, pig, dog, monkey, cattle, horse, sheep, chicken, shark,devilfish, radish, salmon, shrimp, crab or the like may be used.Further, in order to avoid immunorejection, the non-human animal to beused herein is preferably an immunodeficient animal.

Further, the present invention also provides a method of evaluating adrug, comprising using at least one member selected from the groupconsisting of the biological tissue integrated with a vascular system bythe above-described method, the tissue or organ prepared from thevascularized biological tissue, and the non-human chimeric animaltransplanted with the vascularized biological tissue. Specific examplesof drug evaluation include, but are not limited to, evaluation of drugmetabolism (e.g., prediction of drug metabolism profiles), evaluation ofdrug efficacy (e.g., screening for drugs that are effective aspharmaceuticals; confirmation of the effect of pharmaceuticals such asthe relationship between drug efficiency and blood vessels; etc.),toxicity evaluation, and evaluation of drug interactions.

With respect to evaluation of drug efficacy, human-type drug metabolismprofiles may be obtained as follows. Briefly, a biological human tissueintegrated with a vascular system, a human tissue or organ prepared froma biological tissue integrated with a vascular system, or a non-humanchimeric animal transplanted with a biological human tissue integratedwith a vascular tissue is administered with a candidate compound forpharmaceuticals; then, biological samples are taken and analyzed.According to these processes, prediction of thedistribution/metabolism/excretion process of pharmaceuticals inhumans—which has been extremely difficult to achieve by conventionalmethods—becomes possible and one may. expect that the development ofsafe and efficacious pharmaceuticals can be remarkably accelerated.

Screening for drugs that are effective as pharmaceuticals is carried outas follows. Briefly, starting with a tissue induced from a cell/tissueestablished from a diseased patient, a biological tissue integrated witha vascular system, a tissue or an organ prepared from this vascularizedbiological tissue, or a non-human chimeric animal transplanted with thisvascularized biological tissue is prepared. Then, a candidate compoundfor pharmaceuticals is administered for analyses. As a result, one mayexpect that the prediction accuracy of drug efficacy in actualadministration to humans—which has been insufficient in conventional invitro tests—can be greatly improved.

Confirmation of the relationship between drug efficacy and blood vesselsis achieved as follows. Briefly, a biological tissue integrated with avascular system, a tissue or an organ prepared from this vascularizedbiological tissue, or a non-human chimeric animal transplanted with thisvascularized biological tissue is administered with a given drug. Then,the concentration distribution of the drug in tissues at the vicinity ofblood vessels and the desired drug's effect on cells are measured.

In tumor tissues, for example, targeting cancer stem cells which areclinically considered a cause of recurrence or metastasis is believed tobe an important therapeutic strategy. On the other hand, it is knownthat when cancer stem cells are present at the vicinity of bloodvessels, vascular permeability is decreased and anticancer agents aredifficult to infiltrate whereas if they are distant from blood vessels,diffusion of anticancer agents is insufficient. For developing drugstargeting at cancer stem cells, it has been important to reconstitute athree-dimensional tumor tissue that starts from blood vessels and usethis tissue for evaluation. By using the method of the presentinvention, the evaluation of drug efficacy based on cell/tissue polaritywith respect to blood vessels which has been entirely unachievable byconventional methods can be realized and development of drugs withhigher therapeutic effects can be performed.

In the case of toxicity evaluation, a biological tissue integrated witha vascular system, a tissue or an organ prepared from this vascularizedbiological tissue or a non-human chimeric animal transplanted with thisvascularized biological tissue is used as a target which is administereda test substance and thereafter the expressions of tissue disordermarkers are measured, whereby the accuracy in disorder prediction can beimproved.

Development of anticancer agents and other pharmaceuticals that may havetoxicity problems has required huge costs and prolonged periods forevaluating drug toxicity. By creating a micro-environment mimicking theinside of a living body using vascularized tissues, toxicity tests ontissues—which have heretofore been difficult to evaluate—becomeavailable. Briefly, by carrying out toxicity evaluation on bloodvessels, diseased cells and normal cells, one may expect that theresearch and development of new pharmaceuticals can be remarkablyexpedited.

Evaluation of drug interactions may be performed as follows. Briefly, abiological tissue integrated with a vascular system, a tissue or anorgan prepared from this vascularized biological tissue or a non-humanchimeric animal transplanted with this vascularized biological tissue isused as a target which is administered with a plurality of drugs; then,examination of each drug's pharmacokinetics(distribution/metabolism/excretion processes), toxicity evaluation, anddrug efficacy evaluation are performed.

The function level of the cells obtained from pluripotent stem cells byconventional directed differentiation remained less mature in thedifferentiation stage than those functional cells that constitute adulttissues. If, by the method of the present invention, terminallydifferentiated functional cells are obtainable from tissues induced frompluripotent stem cells or the like, it will be a revolutionary techniqueof directed differentiation that serves as an important platform adaptedfor industrial production of human functional cells. For example, humanhepatocytes or human hepatic stem cells isolated from the human livertissues artificially prepared by the present invention will enable massproduction of human adult hepatocytes which are necessary for drugdiscovery and development.

Further, by integrating cancer tissues or normal tissues with stericvascular networks, a revolutionary screening technique will be realizedwhich can evaluate drug efficacy from a totally new viewpoint such asthe correlation between development of drug efficacy and spatialarrangement of blood vessels—a problem that has remained unsolved indrug discovery and development.

Conventionally, medical transplantation targeting such diseases asdiabetes was mainly tissue transplantation therapy involving thetransplantation of islet tissues or the like extracted from bodiesderived from brain-dead donors, for example. However, engraftment oftransplants after the transplantation was remarkably low because thetransplants used in tissue transplantation therapy had no vascularsystem. Thus, the therapeutic effect was rather limited. According tothe present invention, it has become possible to supply vascularizedtransplants that can solve this problem. If industrial production ofhuman tissues/organs for therapeutic purposes that are integrated withvascular networks becomes possible, new tissues/organs fortransplantation which are expected to provide higher therapeutic effectscan be supplied, potentially serving as a revolutionary medicaltechnique.

EXAMPLES

Hereinbelow, the present invention will be described in more detail withreference to the following Examples.

Example 1 Integration of Vascular Networks for Pancreatic Islet Tissues[Methods] 1. Isolation of Mouse Pancreatic Islets

Isolation of mouse pancreatic islets (hereinafter, frequently referredto simply as “islets”) was performed mainly according to the method ofDong et al. (Title of the document: A protocol for islet isolation frommouse pancreas). C57BL/6J mice (Japan SLC, Inc.) anesthetized withdiethyl ether (Wako) were laparotomized after disinfection of theabdomen with 70% ethanol. The ampulla of Vater (that is a joint betweenthe common bile duct and the duodenum) was ligated. Subsequently, a 27 Ginjection needle was inserted into the site of junction of the cysticduct and the hepatic duct, and 3 ml of collagenase XI solution (1,000U/ml) (Sigma, cet. No. C7657) prepared with Hanks' buffer (HBSS, Gibco)was injected to fill the entire pancreas with collagenase XI solution.The pancreas was cut out and placed in a 50 ml tube containingcollagenase XI solution, which was then shaken at 37.5° C. for 15 min.After digestion of the pancreas, 25 ml of ice-cooled HBSS (containing 1mM CaCl₂) was added to the tube for washing. Then, the tube wascentrifuged (290 g, 30 sec, 4° C.), followed by removal of thesupernatant. After re-washing and re-centrifugation, 15 ml of HBSS wasadded to the tube. The resultant content was filtered with a 70 μm meshcell strainer. The residue was entirely transferred into a petri dishusing an originally prepared medium [EGM™ BulletKit™ (Lonza CC-4133)originally modified for the purpose of culturing islets].

2. Selection of Mouse Pancreatic Islets

When the mouse islets isolated in 1 above were observed under astereomicroscope, orange-colored spherical mouse islets (150-250 μm indiameter) could be confirmed. These islets were transferred to an isletculture medium with a Pipetman.

3. Primary Culture of Mouse Pancreatic Islets

Mouse islets were cultured using an originally prepared medium [EGM™BulletKit™ (Lonza CC-4133) supplemented with 10% fetal bovine serum (BWTLot. S-1560), 20 mmol/L L-glutamine (Gibco) and 100 μg/mlpenicillin/streptomycin (Gibco)] in a 37° C. 5% CO₂ incubator.

4. Cell Culture

Normal human umbilical vein endothelial cells (HUVECs) (Lonza CC-2517)were cultured using a medium prepared especially for culturing HUVECs[EGM™ BulletKit™ (Lonza CC-4133)] within a guaranteed passage number (5passages). Human mesenchymal stem cells (hMSCs) (Lonza PT-2501) werecultured using a medium prepared especially for culturing hMSCs [MSCGM™BulletKit™ (Lonza PT3001)] within a guaranteed passage number (5passages). Both HUVECs and hMSCs were cultured in a 37° C., 5% CO₂incubator.

5. Fluorescence Labeling with Retrovirus Vectors

All the gene recombination experiments were performed in P2 level safetycabinets under an approval of the Gene Recombination Committee ofYokohama City University.

Production of virus vectors pGCDΔNsamEGFP and pGCDΔNsamKO was performedby the method described below. Briefly, 293GPG/pGCDΔNsamEGFP cells(kindly provided by Mr. Masafumi Onodera) and 293GPG/pGCDΔNsamKO cells(kindly provided by Mr. Masafumi Onodera) were seeded onpoly-L-lysine-coated dishes and cultured in an especially preparedmedium (designated “293GPG medium”). Briefly, DMEM (Sigma) containing10% fetal bovine serum (Gibco), 2 mmol/L L-glutamine (Gibco), 1×penicillin/streptomycin (Gibco), 1 μg/mL tetracycline hydrochloride(Sigma T-7660), 2 μg/mL puromycin (Sigma P-7255) and 0.3 mg/mL G418(Sigma A-1720) was used. Cultivation was carried out in a 37° C., 10%CO₂ incubator. When cells reached about 80% confluence, the medium wasexchanged with a different medium equivalent to 293GPG medium exceptthat it was freed of tetracycline hydrochloride, puromycin and G418(this medium is designated “293GP medium”) (the day of exchange shall beday 0). After another medium exchange at day 3, the viruses wererecovered together with the medium starting at day 4, followed byfilling with 293GP medium again. The recovered medium was passed througha 0.45 μm filter and stored temporarily at 4° C. The medium recovered upto day 7 by the above-described procedures was centrifuged (6000 G, 4°C., 16 hr). To the resultant pellet, 400 μL of Stempro (Invitrogen) wasadded. After shaking at 4° C. for 72 hr, the resultant solution wasrecovered and stored at −80° C. (designated “100-fold concentrated virussolution”).

HUVECs were cultured until they reached 30-50% confluence. Protamine(Sigma) was added to the medium to give a final concentration of 0.4μm/mL To HUVECs, pGCDΔNsamEGFP was added. Then, cells were infected in a37° C., 5% CO₂ incubator for 4 hr and washed with PBS twice. The mediumwas exchanged with a fresh one, followed by incubation in a 37° C., 5%CO₂ incubator again. These operations were repeated four times and thecells were fluorescence labeled.

6. Examination of Media for Mouse Pancreatic Islets

Media for pancreatic islets were prepared using RPMI1640 (Wako) and anendothelial cell medium (EGM™ BulletKit™) (Lonza CC-4133) separately.One mouse islet was left standing in each well of PrimeSurface™ 96-wellU plates (Sumitomo Bakelite) filled with respective media, followed byincubation in a 37° C. incubator. Subsequently, 20 μl of LIVE/DEAD™ CellImaging Kit (Life Technologies Japan) was added, followed by incubationin a 37° C., 5% CO₂ incubator for 15 min. Then, islets were observedunder a confocal microscope (LEICA TCS-SP5).

7. Preparation of Three-Dimensional Tissues with Human VasculaturesUsing 24-Well Flat Bottom Plate

For the purpose of chronological observation, EGFP-HUVECs (2.0×10⁶cells) and hMSCs (4.0×10⁵ cells) were mixed and centrifuged at 950 rpmfor 5 min. After removal of the supernatant, cells were suspended in 20μl of a medium for islets, and gel was solidified [Briefly, Matrigel(BD) and the medium for islets were mixed at 1:1; the resultant solutionwas poured into each well (300 μl/well); and the plate was left standingin a 37° C., 5% CO₂ incubator for 10 min or more until solidificationoccurred]. Cells were seeded on each well of a 24-well flat bottom plate(BD) in which 300 mouse islets/well had been left standing. Afterseeding, the plate was left standing in a 37° C. incubator for 10 min.After 10 minutes, 1 ml of the medium for islets was added gently downthe well wall, followed by incubation in a 37° C. incubator for one day.

8. Preparation of Three-Dimensional Tissues with Human VasculaturesUsing 96-Well U Plate

Mouse islets were left standing in each well of PrimeSurface™ 96-Well UPlate (Sumitomo Bakelite) preliminarily filled with the medium forislets, and HUVECs and hMSCs were seeded in each well. The plate wassubsequently incubated in a 37° C. incubator for one day.

9. Chronological Observation of Cocultured Cells Using Stereomicroscope

Coculture was performed for tracking chronological changes with astereomicroscope. Briefly, 10 mouse islets were left standing in eachwell of PrimeSurface™ 96-Well U Plate. In each well, HUVECs (1.0×10⁴cells) and hMSCs (1.0×10³ cells) were seeded. After seeding, the platewas mounted in a stereomicroscope (Leica DFC300FX) to observemorphological changes caused by coculture.

10. Validation of Islet Cell's Survival Rates Using Transwell Plate

Mouse islets (30) were left standing in the bottom of each well of24-well Transwell plates. Inserts were placed in other 24-well plates.HUVECs (1×10⁵ cells), hMSCs (2×10⁴ cells) and a mixture of HUVECs (1×10⁵cells) and hMSCs (2×10⁴ cells) were individually seeded in thoseinserts, which were then placed in the 24-well plates where mouse isletshad been left standing. The plates were incubated in a 37° C., 5% CO₂incubator overnight. Subsequently, 200 μl of LIVE/DEAD™ Cell Imaging Kit(Life Technologies, Japan) was added to each well of the 24-well plateswhere mouse islets had been left standing. Then, the plates wereincubated in a 37° C., 5% CO₂ incubator for 15 min, followed byobservation under a confocal microscope (LEICA TCS-SP5).

11. Validation of Islet Cell's Survival Rates Using 96-Well U Plate

Into the medium for the three-dimensional tissue prepared in section 8above, 20 μl of LIVE/DEAD™ Cell Imaging Kit (Life Technologies, Japan)was added, followed by incubation in a 37° C., 5% CO₂ incubator for 15min. Subsequently, cells were observed under a confocal microscope.

12. Quantitative Determination of Insulin Secretion Using TranswellPlate

Mouse islets (100) were left standing in the bottom of each well of24-well Transwell plates. Inserts were placed in other 24-well plates.Inserts in which a mixture of HUVEC (1×10⁵ cells) and hMSC (2×10⁴ cells)was seeded and inserts in which no cell was seeded were prepared. Theseinserts were placed in the 24-well plates where mouse islets had beenleft standing. Then, the plates were incubated in a 37° C., 5% CO₂incubator overnight. Subsequently, supernatant was collected from the24-well plates where mouse islets had been left standing, and subjectedto measurement with an insulin measurement kit (Shibayagi; Cat. No.AKRIN-011H).

13. Glucose Tolerance Test In Vitro

Glucose-free RPMI1640 (Wako) was prepared as a medium for islets. Byadding glucose, a low glucose medium (60 mg/100 ml) and a high glucosemedium (360 mg/100 ml) were created. The low glucose medium was filledin the inserts of 24-well Transwell plate where mouse islets (100) hadbeen left standing. The inserts were transferred to wells where amixture of HUVECs (1×10⁵ cells) and hMSCs (2×10⁴ cells) had been seeded,followed by incubation in a 37° C., 5% CO₂ incubator for 1 hr.Subsequently, the medium in the inserts was exchanged with the highglucose medium, and the inserts were transferred to other wells,followed by incubation in an incubator for 1 hr. After incubation,supernatants from inserts and wells were collected and subjected tomeasurement with an insulin measurement kit (Shibayagi).

14. Experimental Animals

NOD/SCID mice (Sankyo Labo Service Co., Tokyo, Japan) used astransplantation animal were bred under a SPF environment with alight-dark cycle consisting of 10 hours for day and 14 hours for night.The breeding of experimental animals were entrusted to the AnimalExperiment Center, Joint Research Support Section, Advanced MedicalResearch Center, Yokohama City University. Animal experiments wereperformed in accordance with the ethical guidelines stipulated byYokohama City University.

15. Preparation of Cranial Window (CW) Mice for Continuous Observation

Preparation of CW mice was performed mainly according to the method ofYuan et al. (Document Title: Vascular permeability and microcirculationof gliomas and mammary carcinomas transplanted in rat and mouse cranialwindows). For anesthetization, ketalar (Sankyo Yell Yakuhin Co., Tokyo,Japan) 90 mg/kg and xylazine (Sigma Chemical Co., St. Louis, Mo., USA) 9mg/kg were mixed with sterilized PBS to give a dose of 200 μl per mouseand intraperitoneally injected (ketalar/xylazine mixed anesthesia).Ketalar was used according to the Narcotics Administration Law. Afteranesthetization, the hair on the head of NOD/SCID mice was removed withan electric clipper, and each head was sterilized with 70% ethanol.Then, the skin on the head was incised. The periosteum on the surface ofthe skull was removed with cotton swab. Subsequently, the skull wasthinly cut with a dental microdrill (Fine Science Tools, USA) in acircular manner, and the resultant circular portion was removedcarefully. Then, the dura was scraped off with tweezers. When bleedingoccurred, hemostasis was performed with spongel (Astellas Co., Tokyo,Japan). After confirmation of the absence of bleeding, the surface ofthe brain was filled with physiological saline (Otsuka PharmaceuticalCo., Tokyo, Japan). Then, a custom-made circular slide glass 7 mm indiameter (Matsunami, Osaka, Japan) was mounted on the surface and sealedtightly with an adhesive prepared by mixing coatley plastic powder(Yoshida, Tokyo, Japan) with Aron Alpha (Toagosei Co., Tokyo, Japan)until the mixture became cementitious. One week after the preparation ofCW, those mice which did not have any sign of bleeding or inflammationat the site of surgery were selected and used in the subsequentexperiments.

16. Preparation of Diabetes Model Mice

Diabetes model mice were created by administering diphtheria toxin (DT)to SCID Ins-TRECK-Tg mice (kindly provided by Tokyo MetropolitanInstitute for Clinical Medicine). DT 1 μg/kg was adjusted withphysiological saline to give a dose of 200 μl per mouse and injectedintraperitoneally. After administration, regular glucose level and bodyweight were measured every day at 17:00. Those mice which had a regularglucose level reading of 300 mg/dl for consecutive three days or morewere used as diabetes model mice. Measurement of glucose levels wasperformed by Glutest neo Sensor™ (Panasonic, Tokyo) on blood samplestaken from the tail vein.

17. Transplantation into CW Mice

The CW mice prepared in Section 15 above underwent transplantation aftertheir brain surfaces were exposed by removing the glass of the cranialwindow. Those mice which did not have any sign of bleeding, inflammationor infection on their brain surfaces were used. After anesthetization,the area surrounding the cranial window was disinfected with 70%ethanol. The pointed end of an 18G needle was inserted into the borderline between the custom-made circular slide glass and Aron Alpha and somanipulated as to peel off the slide glass without damaging the brainsurface. Thus, the brain surface was exposed. Subsequently, the brainsurface was washed with physiological saline. A tissue transplant wasleft standing near the center of the brain surface, and the slide glasswas remounted. To ensure no gap would be left, the space between theslide glass and the brain surface was filled with physiological salineand thereafter the slide glass was sealed tightly with an adhesiveprepared from coatley plastic powder and Aron Alpha, in the same manneras performed at the time of preparation of CW mouse.

18. Transplantation into the Subcapsular Space of the Kidney

The diabetes model mice prepared in Section 16 above were anesthetizedwith isoflurane using an anesthetizing device for experimental animals(Shinano). Subsequently, the hair in the left half of the back of eachmouse was removed with an electric clipper. After the shaven site wasdisinfected with 70% ethanol, the kidney was exposed by 1.5-2 cmincision. After exposure, the kidney was fixed and the capsule on theventral side of the kidney was partially incised. Through the resultantopening, three-dimensional tissues prepared in Section 7 above weretransplanted. After transplantation, the kidney was returned into thebody. Then, the fascia and the skin were sutured.

19. Periodical observation with Confocal Microscope of the TissuesTransplanted into CW Mice

The three-dimensional tissues transplanted into CW mice in Section 17above were observed.

Those mice which underwent transplantation were anesthetized byketalar/xylazine mixed anesthesia in the same manner as in Section 11above. Each mouse was fixed on a 25×60 mm micro cover glass (Matsunami)in the supine position so that the cranial window would become level.Morphological changes of the transplanted three-dimensional tissues withvascular networks were observed with a confocal microscope (LEICATCS-SP5).

19-1 Visualization of Mouse Blood Flow

In order to visualize the blood flow from them, the host mice thatunderwent transplantation were anesthetized in the same manner as inSection 15 above. A fluorescent dye prepared by mixing fluoresceinisothio-cyanate-dextran (Sigma, USA) with physiological saline wasadministered to each mouse at a rate of 100 μl per 20 g body weight fromthe tail vein using Myjector 29G. Subsequently, observation wasperformed in the same manner as described in Section 19 above.

19-2 Visualization of Host Derived Vascular Endothelial Cells

In order to visualize host-derived blood vessels among the vascularnetworks constructed in the transplanted cells, mice were anesthetizedin the same manner as in Section 15, followed by injection ofAlexa-Flour 647 anti-mouse CD31 (Biolegend) antibody at a rate of 100 μlper 20 g body weight from the tail vein using a 29G syringe.Subsequently, observation was performed in the same manner as describedin Section 19 above.

20. Visualization of Normal Islet Tissues

The internal structure of normal islet tissues was visualized usingPdx-DsRed mice (kindly provided by Mr. Douglous Melton) and CAG-GFP mice(Japan SLC). The mice were anesthetized with isoflurane using ananesthetizing device for experimental animals. The hair on the back ofeach mouse was removed with an electric clipper. Then, each mouse wasincised in the back by 0.5-1 cm so that the spleen was exposed to theoutside, whereupon the pancreas adhering in the vicinity of the spleenbecame exposed. After this exposure, each mouse was held in a 10 cm dishsuch that the pancreas stuck to the bottom. With each mouse held in thisposition, 1.5% agarose gel solution cooled to 37° C. was poured into thedish to thereby fix the mouse as the pancreas remained exposed. Normalislet tissues in the fixed mouse were observed with a confocalmicroscope.

21. Glucose Tolerance Test In Vivo

A glucose solution 3 g/kg was adjusted with physiological saline to givea dose of 200 μl per mouse and administered by intraperitonealinjection. After administration, blood samples were taken from the tailvein every 15 min and measured for glucose levels with a Glutest neoSensor™ (Panasonic, Tokyo).

22. Preparation of Frozen Sections

Transplanted samples were removed, washed with PBS and fixed in 4%paraformaldehyde for 1 day. Then, the sample tissue was transferred into10% and 20% sucrose solutions, and kept there until it sank (sucrosereplacement). The sinking tissue was transferred from the 20% sucrosesolution to a 30% sucrose solution and kept there for 1 day for sucrosereplacement. The resultant sample tissue was embedded in O.C.T. compound(Funakoshi Co.), followed by infiltration at 4° C. for 15 min.Subsequently, the sample tissue was mounted on a stand of aluminum foilfloating on liquid nitrogen for freezing.

The resultant frozen block was sliced thinly into 5 μm thick sectionswith a cryostat (Lwica CM1950) and adhered onto a slide glass(Matsunami) Frozen sections were air-dried before use.

23. Preparation of Paraffin Sections

Transplanted samples were removed, washed with PBS and fixed in 4% PFAfor 1 day. After fixation, the sample was washed with PBS three times,and dehydrated with 50, 70, 80, 90, 95 or 100% ethanol for 1 hr at eachconcentration. After 1 hr dehydration with 100% ethanol, the sample wasdehydrated with fresh 100% ethanol for 1 day. The resultant sample wassubjected to xylene replacement three times, each for 1 hr andtransferred into a thermostat bath for paraffin embedding that was setat 65° C., where the sample was infiltrated with a paraffin:xylene (1:1)mixture for 1 hr and with paraffin three times, each for 2 hr. Afterinfiltration, the sample was embedded in paraffin to prepare a paraffinblock.

The thus prepared paraffin block was sliced on a microtome thinly into 5μm thick sections, which were used as paraffin sections.

24. HE (Haematoxylin/Eosin) Staining

Frozen sections were washed with tap water for 2 min to remove the OCTcompound. After washing with deionized water, tissue sections werenuclear-stained with haematoxylin (Wako) for 9 min. Subsequently, thestain solution was washed out with deionized water. The resultant tissuesections were soaked in tap water for 10 min to effect water extraction.Subsequently, after washing with deionized water, the cytoplasm oftissue sections was stained with eosin (Muto Chemical) for 10 min. Afterremoving the excessive eosin with deionized water, tissue sections weredehydrated with a series of ethanol baths at increasing concentrations,cleared with xylene, and shielded.

Paraffin sections were infiltrated with 100% xylene three times, eachfor 5 min and then soaked in 100, 90, 80, 70, 60 or 50% ethanol for 3min at each concentration to effect deparaffinization that rendered thesections hydrophilic. Subsequently, similar to the frozen sectionsdescribed above, the hydrophilic sections were washed with deionizedwater and, thereafter, HE staining was performed.

25. Immunohistochemical Staining

After OCT removal and deparaffinization, tissue sections were eachwashed with PBS three times for 5 min and fixed in 4% PFA for 10 min at4° C. Subsequently, the tissue sections were washed with PBS three timesfor 5 min, and blocked at 4° C. overnight with a blocking solutioncontaining 10% normal serum of an animal used for secondary antibodypreparation (goat). Then, a primary antibody diluted 200-fold with PBSwas added and after reaction at 4° C. overnight, the sections werewashed with PBS three times for 5 min. As the primary monoclonalantibody, a combination of anti-mouse/guinea pig insulin antibody,anti-human/mouse CD31, anti-mouse/rat CD31, anti-human/mouse collagen 4,anti-human/rabbit laminin antibody, and anti-mouse/rabbit caspase-3antibody was used. Further, a secondary antibody diluted 500-fold withPBS was added to the tissue sections and after reaction at roomtemperature under shading conditions for 1 hr, the tissue sections werewashed with PBS three times for 5 min, shielded with a mounting mediumcontaining 4′,6-diamidino-2-phenylindole dihydrochloride (DAPI;Invitrogen), and observed and photographed with a fluorescencemicroscope. As the secondary antibody (Molecular Probe), a combinationof the following antibodies was used: Alexa 488-, 555-labeled goatanti-rabbit IgG_((H+L)) antibody, Alexa 488-, 555-, 647-labeled goatanti-rat IgG_((H+L)) antibody, Alexa 488-, 555-labeled goat anti-guineapig IgG_((H+L)) antibody, and Alexa 488-, 555-, 647-labeled goatanti-mouse IgG_((H+L)) antibody.

26. Immunohistological Analysis by Whole Mount Method

Vascularized islets as generated were recovered and fixed in a 4% PFAsolution for 1 day, followed by washing with PBS three times for 10 min.After fixation, the islets were placed in a 0.1% Triton-PBS solutioncontaining 3% BSA and blocked at room temperature for 1 hr. Afterblocking, the islets were washed with a 0.1% Triton-PBS solution threetimes for 10 min. A transplant was placed in a solution of primaryantibody diluted with a 0.1% Triton-PBS solution and reaction wasperformed at 4° C. for 1 day. After the reaction, the transplant waswashed with a 0.1% Triton-PBS solution three times for 10 min and thenplaced in a solution of secondary antibody diluted with a 0.1%Triton-PBS solution, followed by reaction at room temperature for 4 hr.After the reaction, the transplant was washed with a 0.1% Triton-PBSsolution three times for 10 min. A mounting medium containing DAPI wasadded to the transplant, which was then observed with a confocalmicroscope.

[Results] 1. Generation of Three-Dimensional Tissues by CoculturingMouse Islets, Vascular Endothelial Cells and Mesenchymal Stem Cells

Media were validated using the survival rate of islet cells as anindicator (FIG. 1A). At 72 hours of culture, dead cell numbers per isletarea under respective conditions were 14 cells/mm² in RPMI1640 medium;1.8 cells/mm² in the mixed medium of RPMI1640 and the endothelial cellmedium; and 0.8 cells/mm² in the endothelial cell medium (FIG. 1B).

Culture was performed as described in Section 7 of Methods above.Immediately after the beginning of culture, cells were scattered aroundislets and no three-dimensional tissues visible with eyes wererecognized. At 4 hours of culture, however, interactions between cellsstarted, and scattered cells began to gather closely. At 8 hours ofculture, cells so aggregated as to cover islets and graduallyconstituted a three-dimensional structure. Finally, at 24 hours ofculture, self-organization progressed further and a vascularizedthree-dimensional tissue was constituted (FIG. 1C, upper panel; FIG.1E). On the other hand, when coculture was not performed but isletsalone were cultured, neither vascularization nor formation ofthree-dimensional tissues was recognized (FIG. 1D).

Further, by culturing islets as described in Section 8 of Methods above,an attempt was made to decrease the size of vascularizedthree-dimensional tissues in a culture plate (substrate?) of such ashape that cells/tissues would gather in the bottom (FIG. 2). When 1, 5,10 and 20 mouse islet tissues were cocultured with HUVECs and MSCs,three-dimensional tissues were formed at 24 hours of culture and theirmorphology was retained even at 48 hours of culture (FIG. 2A). Further,minimum cell numbers of HUVECs and MSCs required for constitution of avascularized three-dimensional tissue were examined (FIG. 2B). When 10mouse islets were cocultured with 1.0×10⁴ HUVECs and 1.0×10³ MSCs,scattered cells began to aggregate due to the intercellular adhesion at2 hours of culture. At 9 hours of culture in an advanced stage, cells soaggregated as to cover islets until they constituted a three-dimensionaltissue (FIG. 2C, left panel). In order to track morphological changes incells, coculture experiments were performed using fluorescence-labeledmouse islets and various kinds of cells (FIG. 1A, lower panel; FIG. 2C,right panel; FIG. 2D). Briefly, islets isolated from Pdx-DsRed mice(FIG. 1A; 2D: red; 2C: blue), HUVECs into which green fluorescentprotein (GFP) had been introduced (FIG. 1A, 2C, 2D: green) and MSC (FIG.2C: red) were cocultured, followed by observation of cell morphologyunder a confocal microscope. Immediately after the beginning of culture,HUVECs were found to be scattered evenly around islets. Further, HUVECswere shown not only to adhere directly to islet tissues; some of themwere also shown to connect to vascular endothelial cells inside theislets (FIG. 2E).

From the foregoing, it was revealed that a vascularizedthree-dimensional tissue was autonomously generated by coculturing thethree types of cells, i.e., mouse islet, HUVEC and MSC, underappropriate conditions.

2. Improvement of the Function of Mouse Islet by Coculture with VascularEndothelial Cells and Mesenchymal Stem Cells

Mouse islets were cultured as described in Section 10 of Methods aboveand their survival rates under various conditions were compared (FIG.1F, viable cell: green; dead cell: red). At 24 hours of culture, deadcell numbers per islet area under the respective conditions were 53cells/mm² in monoculture of islets alone, 14 cells/mm² in coculture withHUVECs, 2 cells/mm² in coculture with MSCs, and 0.1 cells/mm² incoculture with HUVECs and MSCs (FIG. 1G). From these results, it wasshown that the survival rate of mouse islet cells was improved bycoculturing with HUVECs and MSCs.

Further, culture was performed as described in Section 12 of Methodsabove and insulin levels secreted from the mouse islets were measured(FIG. 1H). At 24 hours of culture, the insulin secretion from the mouseislets cocultured with HUVECs and MSCs was greater than that from themonocultured mouse islets. When a glucose tolerance test was performedin vitro, insulin secretion increased 1.37-fold in the islet monoculturegroup and 1.97-fold in the coculture group (FIG. 1I). In order tospecify the group of molecules contributing to such improvement of isletfunction, changes in gene expressions before and after coculture withHUVCs and MSCs were analyzed comprehensively by microarray analysis. Asa result, 214 candidate genes were extracted as genes whose expressionwas enhanced by coculture by a factor of two or more (FIG. 1J). It wastherefore suggested that coculturing mouse islets with HUVECs and MSCsinitiated changes in the expression of various genes, leading to animprovement of the function of the mouse islets.

3. Periodical Observation of Vascularized Islet Transplantation

The vascularized islet generated in Section 1 of Results above wastransplanted into mice and morphological changes in tissues were tracked(FIG. 3). Further, in order to examine the necessity of vascularizationfor generating tissues, mouse islets alone were transplanted into micefor comparison. Vascularized islets were transplanted into cranialwindow (CW) mice as described in Section 17 of Methods, andmorphological changes were tracked as described in Section 19 ofMethods.

After transplantation of mouse islets alone, no macroscopic changes wereobserved in mouse heads until day 2 post-transplantation. Also, no bloodperfusion into transplanted islets was observed. As time passed aftertransplantation, viable islets decreased (FIG. 3B). When fluorescencelabeling was used to observe changes in cell morphology, there were nochanges, either, but the number of islets gradually decreased. Further,when blood flow was visualized, no blood perfusion into the inside ofislets occurred at day 7 post-transplantation (FIG. 3D, islet: green;blood flow: red). However, in the mouse heads transplanted withvascularized islets, blood perfusion to all over the transplantationsite occurred at day 2 post-transplantation (FIG. 3A). Further,according to an observation with a confocal microscope, blood perfusioninto the inside of islets was confirmed at day 7 post-transplantation(FIG. 3C, islet: green; blood flow: red).

It was shown by these results that transplantation of vascularizedislets induced early resumption of blood flow into the inside of thetransplanted islets and improved the islet survival rate aftertransplantation.

4. Validation of Therapeutic Effect on Diabetes by Transplantation ofVascularized Islets

Forty vascularized islets cocultured under the condition of 5 isletswere transplanted into the subcapsular space of the kidney of diabetesmodel mice and evaluated for their therapeutic effects (FIG. 3E).Decrease in glucose level was seen at day 1 post-transplantation, andnormal glucose level was kept stably retained at week 2post-transplantation and thereafter (FIG. 3F). Further, a great increasein body weight was seen (FIG. 3G) and survival rate improved (FIG. 3H).The results of a glucose tolerance test in vivo revealed that thediabetes model mice showed a insulin secretion response which was almostequal to that of normal mice (FIG. 3I).

As described above, therapeutic effects on diabetes were shown bytransplanting vascularized islets.

5. Histological Analysis of Vascularized Islets

Vascularized islets at day 1 of coculture were analyzed histologicallyand immunohistologically. When HE staining was performed, islet tissueswere observed that had no central necrosis and which adjoined HUVECs andMSCs (FIG. 2E, upper panel). Further, immunostaining was performed asfollows (FIG. 1E′; 2E, lower panel). Briefly, islets were stained withinsulin antibodies (FIG. 1E′: green; 2E: red); HUVECs were stained withhuman vascular endothelial cell antibodies (FIG. 1E′: red; 2E: green);and mouse blood vessels were stained with mouse vascular endothelialcell antibodies (FIG. 2E: blue). The presence of HUVECs was confirmed inthe inside of insulin-positive islets, and HUVECs and mouse bloodvessels were connected together.

Further, vascularized islets (FIG. 3J) and islets (FIG. 3K) at day 30post-transplantation into cranial windows were individually analyzedhistologically and immunohistologically. As a result of HE staining,islets engrafting onto the brain tissue were confirmed. As a result ofimmunostaining, it was found that human vascular endothelial cells werepresent at insulin-positive sites in the vascularized islets, and thatsuch human vascular endothelial cells were stable human blood vesselsthat would secrete laminin and collagen IV (extracellular matrices).However, when islets alone were transplanted, no vascular endothelialcells were found inside the islets.

Further, vascularized islets (FIG. 3L) and islets (FIG. 3M) at day 28post-transplantation into the subcapsular space of the kidney wereindividually analyzed histologically and immunohistologically. As aresult of HE staining, islets present between the renal parenchyma andthe capsule were confirmed (FIG. 3L, lower left panel; FIG. 3M, lowerleft panel). Further, immunostaining was performed to stain islets(green) with an insulin antibody and vascular endothelial cells (red)with a laminin antibody (FIG. 3L, lower right panel; FIG. 3M, lowerright panel). In the vascularized inlets, expression of laminin-positivevascular endothelial cells was confirmed inside insulin-positive islets.However, in those islets which were transplanted with inlets alone, novascular endothelial cells were observed.

As described above, it was shown from histological andimmunohistological viewpoints that the vascularized islets were islettissues associated with human blood vessels.

Example 2 Integration of Vascular Networks for Renal Glomeruli[Methods] 1. Isolation of Mouse Glomeruli

C57BL/6-Tg mice (Japan SLC, Inc.) anesthetized with diethyl ether (Wako)were laparotomized after disinfection of the abdomen with 70% ethanol.The kidney was cut out and the capsule was removed therefrom. Afterwashing with physiological saline, the kidney was cut in round sliceswith a scalpel. The renal pelvis and the medulla were removed withscissors, and the cortex was recovered. The recovered cortex was mincedon ice and filtered with a 100 μm mesh cell strainer while adding Hanks'buffer (HBSS, Gibco) containing 0.1% albumin from bovine serum (BSA,Sigma) little by little. The flow-through was filtered with a 70 μm meshcell strainer, and finally the flow-through was filtered with a 40 μmmesh cell strainer. The cell mass retained on the 40 μm mesh cellstrainer was recovered with 0.1% BSA-containing Hanks' buffer. The thusrecovered material was filtered with a 100 μm mesh cell strainer.

2. Selection of Mouse Glomeruli

When the mouse glomeruli isolated in Section 1 of Methods above wereobserved under a stereomicroscope, spherical mouse glomeruli (diameter:50-100 μm) could be confirmed. These glomeruli were recovered andtransferred to a medium for glomeruli with a Pipetman.

3. Primary Culture of Mouse Glomeruli

Mouse glomeruli were cultured using RPMI1640 (Wako) supplemented with20% fetal bovine serum (BWT Lot. S-1560), 100 μg/mlpenicillin/streptomycin (Gibco) and Insulin-Transferrin-SeleniumX(Gibco) in a 37° C., 5% CO₂ incubator.

4. Cell Culture

Normal human umbilical vein endothelial cells (HUVECs) (Lonza CC-2517)were cultured using a medium prepared especially for culturing HUVEC[EGM™ BulletKit™ (Lonza CC-4133)] within a guaranteed passage number (5passages). Human mesenchymal stem cells (hMSCs) (Lonza PT-2501) werecultured using a medium prepared especially for culturing hMSCs [MSCGM™BulletKit™ (Lonza PT3001)] within a guaranteed passage number (5passages). Both HUVECs and hMSCs were cultured in a 37° C., 5% CO₂incubator.

5. Preparation of Three-Dimensional Tissues Having a Vascular System

For the purpose of chronological observation, 1, 5 and 10 mouseglomeruli/well were left standing in each well of PrimeSurface™ 96-WellU Plate (Sumitomo Bakelite) preliminarily filled with a medium forglomeruli, and 5×10⁴ HUVECs and 5×10³ hMSCs were seeded in each well.Subsequently, the plate was incubated in a 37° C. incubator for one day.Further, 100 mouse glomeruli/well were left standing in each well of a24-well plate, and 2×10⁶ HUVECs and 2×10⁵ hMSCs were seeded in eachwell.

6. Chronological Observation Using Stereomicroscope

Coculture was performed for tracking chronological changes with astereomicroscope. Briefly, 20 mouse glomeruli/well were left standing ineach well of a 24-well plate, and 2×10⁶ HUVECs and 2×10⁵ hMSCs wereseeded in each well. After seeding, the plate was set in astereomicroscope (Leica DFC300FX) and morphological changes caused bycoculture were observed.

7. Experimental Animals

NOD/SCID mice (Sankyo Labo Service Co., Tokyo, Japan) used astransplantation animal were bred under a SPF environment with alight-dark cycle consisting of 10 hours for day and 14 hours for night.The breeding of experimental animals were entrusted to the AnimalExperiment Center, Joint Research Support Section, Advanced MedicalResearch Center, Yokohama City University. Animal experiments wereperformed in accordance with the ethical guidelines stipulated byYokohama City University.

8. Transplantation into CW Mice

The CW mice prepared underwent transplantation after their brainsurfaces were exposed by removing the glass of the cranial window. Thosemice which did not have any sign of bleeding, inflammation or infectionon their brain surfaces were used. After anesthetization, the areasurrounding the cranial window was disinfected with 70% ethanol. Thepointed end of an 18G needle was inserted into the border between thecustom-made circular slide glass and Aron Alpha and so manipulated topeel off the slide glass without damaging the brain surface. Thus, thebrain surface was exposed. Subsequently, the brain surface was washedwith physiological saline. A tissue transplant was left standing nearthe center of the brain surface, and the custom-made slide glass wasremounted. To ensure no gap would be left, the space between the slideglass and the brain surface was filled with physiological saline andthereafter the slide glass was sealed tightly with an adhesive preparedfrom coatley plastic powder and Aron Alpha, in the same manner asperformed at the time of preparation of CW mice.

9. Periodical observation_with Confocal Microscope of the TissuesTransplanted into CW Mice

The three-dimensional tissues transplanted into the CW mice in thepreceding Section 8 were observed.

Those mice which underwent transplantation were anesthetized byketalar/xylazine mixed anesthesia in the same manner as in Section 11above. Each mouse was fixed on a 25×60 mm micro cover glass (Matsunami)in the supine position so that the cranial window would become level.Morphological changes of the transplanted three-dimensional tissues withvascular networks were observed with a confocal microscope (LEICATCS-SP5).

[Results] 1. Generation of Vascularized Three-Dimensional Tissues byCoculture of Mouse Glomeruli, Vascular Endothelial Cells and MesenchymalStem Cells

Culture was performed as described in Section 6 of Methods above.Immediately after the beginning of culture, cells were scattered aroundglomeruli and no three-dimensional tissues visible with eyes wererecognized. At 4 hours of culture, however, interactions between cellsstarted, and scattered cells began to gather closely. At 8 hours ofculture in an advanced stage, cells so aggregated as to cover glomeruliand gradually constituted a three-dimensional structure. Finally, at 24hours of culture, self-organization progressed further and avascularized three-dimensional tissue was constituted (FIG. 4A, 4B). Onthe other hand, when coculture was not performed but glomeruli alonewere cultured, neither vascularization nor formation ofthree-dimensional tissues was recognized (FIG. 4C).

Further, by culturing glomeruli as described in Section 5 of Methodsabove, an attempt was made to decrease the size of vascularizedthree-dimensional tissues in a culture plate (substrate?) of such ashape that cells/tissues would gather in the bottom (FIG. 4C). When 5,10 and 15 mouse glomeruli were individually cocultured with HUVECs andMSCs, three-dimensional tissues were formed at 24 hours of culture. Inorder to track morphological changes in cells, fluorescence-labeledmouse glomeruli were cocultured with various kinds of cells (FIGS. 4B,4C and 4D). Briefly, glomeruli isolated from mice (green), HUVECs intowhich Kusabira Orange had been introduced (FIGS. 4B, 4C and 4D: red) andMSCs (FIGS. 4B and 4D: blue) were cocultured, and cell morphology wasobserved with a confocal microscope. It was observed that, immediatelyafter the beginning of culture, HUVECs were found to be scattered evenlyaround glomeruli.

From the foregoing, it was revealed that a vascularizedthree-dimensional tissue was autonomously generated by coculturing thethree types of cells, i.e. mouse glomeruli, HUVEC and MSC, underappropriate conditions.

2. Periodical Observation of Vascularized Glomeruli Transplantation

The vascularized glomeruli generated in Section 1 of Results above weretransplanted into mice and morphological changes in tissues were tracked(FIG. 4E). Vascularized glomeruli were transplanted into cranial window(CW) mice as described in Section 8 of Methods, and morphologicalchanges were tracked as described in Section 9 of Methods.

In the mouse heads transplanted with the vascularized glomeruli, bloodperfusion to all over the transplantation site occurred at day 3post-transplantation (FIG. 4E). Further, the results of live observationwith a confocal microscope at day 10 post-transplantation not onlyrevealed that the glomerular structure was retained even aftertransplantation; it was also found that mouse blood vessels insideglomeruli were directly anastomosed to human blood vessels (HUVECs),letting blood flow inside the glomeruli (FIG. 4F). These results showthat transplantation of vascularized glomeruli induced early resumptionof blood flow into the glomeruli and enabled efficient engraftment.

Example 3 Integration of Vascular Networks for Tumor Tissues[Methods] 1. Recovery of Human Pancreatic Tumor Tissues

Human pancreatic tumor tissues removed from nesidioblastosis patientswere washed with PBS under a clean bench environment, transferred to a 6cm dish containing a HBSS medium and sliced into 1 mm-square sections,which were used in the subsequent experiments.

2. Integration of Vascular Networks for Human Pancreatic Tumor Tissues

Human pancreatic tumor tissues sliced into 1 mm-square sections wererecovered with a Pipetman (20 sections) and mixed with 2×10⁶ EGFP-HUVECsand 2×10⁵ MSCs. The mixture was centrifuged at 950 rpm. The resultantsupernatant was removed, and the cells were suspended in 1 ml of EGMmedium and seeded on 24-well plate in which Matrigel was placed inadvance. Then, morphological changes were tracked with a confocalmicroscope.

3. Recovery of Mouse Pancreatic Cancer Tissues

Pancreatic cancer tissues were recovered from pancreatic cancer modelmice (Pdx1-cre; LSL-Kras^(G12D); CDKN2A^(−/−): purchased from NCI) whichare held to be capable of recapitulating the multistep carcinogenesis ofpancreatic cancer. The cancer tissues were washed with PBS andtransferred to a 6 cm dish containing a HBSS medium under a clean benchenvironment. The recovered cancer tissues were chopped into 1 mm-squaresections, which were used in the subsequent experiments.

4. Integration of Vascular Networks for Mouse Pancreatic Cancer Tissues

Pancreatic cancer tissues chopped into 1 mm-square sections wererecovered with a Pipetman (20 sections) and mixed with 2×10⁶ EGFP-HUVECsand 2×10⁵ MSCs. The mixture was centrifuged at 950 rpm for 5 min. Theresultant supernatant was removed, and the cells were suspended in 1 mlof EGM™ BulletKit™ (Lonza CC4133) medium and seeded on 24-well plate inwhich Matrigel was placed in advance. The plate was incubated in a 37°C. incubator for 4 days while exchanging the medium every day.

The 24-well plate was prepared as follows. Briefly, 300 μl of a solutionprepared by mixing EGM medium and BD Matrigel™ basement membrane matrix(BD Japan 356234) at 1:1 was added to each well of a 24-well plate,which was then incubated in a 37° C. incubator for 10 min to solidifythe gel.

[Results] 1. Vascularization of Human Pancreatic Tumor Tissues

The results of observation with a confocal microscope confirmed that bymeans of coculture, vascularized three-dimensional tissues wereautonomously generated in about 24-48 hours while vascular networks wereconstituted around the human pancreatic tissues chopped into 1 mm-squaresections (FIG. 5A).

2. Vascularization of Mouse Pancreatic Cancer Tissues

When the pancreatic cancer tissue chopped into 1 mm-square sections wascocultured with HUVECs and MSCs on the Matrigel™ solidified in 24-wellplate, vascularized three-dimensional tissues could successfully begenerated (FIG. 5B, upper panel). As a control experiment, 1 mm-squaresections of the pancreatic cancer tissue alone were cultured onsolidified Matrigel™; neither formation of three-dimensional tissues norvascularization was confirmed and there occurred no changes worthparticular mention (FIG. 5B, lower panel).

At 4 days of culture, gene expressions in the vascularizedthree-dimensional tissues formed were analyzed by quantitative PCR. Theresult revealed that the expression of CD44 gene known as an importantcancer stem cell marker increased to a level about 1.6 times as high asthe level of expression in the monoculture group (FIG. 5C).

It was therefore suggested that cancer stem cells—which wereconventionally difficult to maintain in vitro—were amplified.Conventional two-dimensional culture systems were difficult to use as asystem for pre-evaluating the efficacy of anticancer agents because thetwo-dimensional system has such an environment that the reactivity ofanticancer agents differs greatly from the case where they areadministered in vivo. By using the method of the present invention, itis expected to reproduce the reactivity in cancer tissues (includingvascular systems) in living bodies. This is a culture technique that ispotentially highly useful as a drug screening system applicable to thedevelopment of novel anticancer agents.

Example 4 Integration of Vascular Networks for Liver Tissues[Methods] 1. Isolation of Mouse Liver Tissues

C57BL/6-Tg mice (Japan SLC, Inc.) anesthetized with diethyl ether (Wako)were laparotomized after disinfection of the abdomen with 70% ethanol,followed by transcardial perfusion. The liver was cut out, washed withphysiological saline and minced with scissors. The minced liver wasfiltered with a 100 μm mesh cell strainer while adding Hanks' buffer(HBSS, Gibco) containing 0.1% albumin from bovine serum (BSA, Sigma)little by little. The flow-through was filtered with a 70 μm mesh cellstrainer. The cell mass retained on the 70 μm mesh cell strainer wasrecovered with a 0.1% BSA-containing Hanks' buffer.

2. Primary Culture of Mouse Liver Tissues

Mouse liver tissues were cultured in DMEM/F12 (Invitrogen) supplementedwith 10% fetal bovine serum (ICN Lot. 7219F), 2 mmol/L L-glutamine(Gibco), 100 μg/mL penicillin/streptomycin (Gibco), 10 mmol/Lnicotinamide (Sigma), 50 μmol/L 2-Mercaptoethanol, 1×10⁻⁷ mol/L 6.5%dexamethasone (Sigma), 2.6×10⁻⁴ M L-Ascorbic acid 2-phosphatesesquimagnesium salt hydrate (Sigma), 5 mmol/L HEPES (DOJINDO), 1 μg/mLHuman recombinant insulin expressed in yeast (Wako), 50 ng/mL Humanrecombinant HGF expressed in Sf21 insect cells (Sigma) and 20 ng/mLMouse Submaxillary Glands EGF (Sigma) in a 37° C., 5% CO₂ incubator.

3. Cell Culture

Normal human umbilical vein endothelial cells (HUVECs) (Lonza CC-2517)were cultured using a medium prepared especially for culturing HUVECs[EGM™ BulletKit™ (Lonza CC-4133)] within a guaranteed passage number (5passages). Human mesenchymal stem cells (hMSCs) (Lonza PT-2501) werecultured using a medium prepared especially for culturing hMSCs [MSCGM™BulletKit™ (Lonza PT3001)] within a guaranteed passage number (5passages). Both HUVECs and hMSCs were cultured in a 37° C., 5% CO₂incubator.

4. Preparation of Three-Dimensional Tissues with Vascular Networks

For chronological observation, two mouse liver tissues were leftstanding in each well of PrimeSurface™ 96-well U plate (SumitomoBakelite) preliminarily filled with a medium for liver tissues. Then,5×10⁴ HUVECs and 5×10³ hMSCs were seeded in each well. The plate wasthen incubated in a 37° C. incubator for 1 day.

5. Experimental Animals

NOD/SCID mice (Sankyo Labo Service Co., Tokyo, Japan) used astransplantation animal were bred under a SPF environment with alight-dark cycle consisting of 10 hours for day and 14 hours for night.The breeding of experimental animals were entrusted to the AnimalExperiment Center, Joint Research Support Section, Advanced MedicalResearch Center, Yokohama City University. Animal experiments wereperformed in accordance with the ethical guidelines stipulated byYokohama City University.

6. Transplantation into CW Mice

The CW mice prepared in Section 8 above underwent transplantation aftertheir brain surfaces were exposed by removing the glass of the cranialwindow. Those mice which did not have any sign of bleeding, inflammationor infection on their brain surfaces were used. After anesthetization,the area surrounding the cranial window was disinfected with 70%ethanol. The pointed end of an 18G needle was inserted into the borderline between the custom-made circular slide glass and Aron Alpha and somanipulated as to peel off the slide glass without damaging the brainsurface. Thus, the brain surface was exposed. Subsequently, the brainsurface was washed with physiological saline. A tissue transplant wasleft standing near the center of the brain surface, and the slide glasswas remounted. To ensure no gap would be left, the space between theslide glass and the brain surface was filled with physiological salineand, thereafter, the slide glass was sealed tightly with an adhesiveprepared from coatley plastic powder and Aron Alpha, in the same manneras performed at the time of preparation of CW mouse.

7. Periodical Observation with Confocal Microscope of the TissuesTransplanted into CW Mice

The three-dimensional tissues transplanted into CW mice in Section 6above were observed.

Those mice which underwent transplantation were anesthetized byketalar/xylazine mixed anesthesia in the same manner as in Section 11above. Each mouse was fixed on a 25×60 mm micro cover glass (Matsunami)in the supine position so that the cranial window would become level.Morphological changes of the transplanted three-dimensional tissues withvascular networks were observed with a confocal microscope (LEICATCS-SP5).

[Results] 1. Generation of Three-Dimensional Tissues by CoculturingMouse Liver Tissues, Vascular Endothelial Cells and Mesenchymal StemCells

Culture was performed as described in Section 4 of Methods above.Immediately after the beginning of culture, cells were scattered aroundliver tissues, and no three-dimensional tissues visible with eyes wererecognized. At 4 hours of culture, however, interactions between cellsstarted, and scattered cells began to gather closely. At 8 hours ofculture in an advanced stage, cells so aggregated as to cover livertissues and gradually constituted a three-dimensional structure.Finally, at 24 hours of culture, self-organization progressed furtherand a vascularized three-dimensional tissue was constituted (FIG. 6A,6B). On the other hand, when coculture was not performed but livertissues alone were cultured, neither vascularization nor formation ofthree-dimensional tissues was recognized (FIG. 6B).

Further, by culturing cells as described in Section 4 of Methods above,an attempt was made to decrease the size of vascularizedthree-dimensional tissues in a culture plate (substrate?) of such ashape that cells/tissues would gather in the bottom (FIG. 6A). Whenmouse liver tissues were cocultured with HUVECs and MSCs,three-dimensional tissues were formed at 24 hours of culture. In orderto track morphological changes in cells, coculture experiments wereperformed using fluorescence-labeled mouse liver tissues and variouskinds of cells (FIG. 6A). Briefly, liver tissues isolated from mice(FIG. 6A: red; 6B, 6D: green), HUVECs into which green fluorescentprotein (GFP) had been introduced (FIG. 6B) and MSCs were cocultured,followed by observation of cell morphology under a confocal microscope.Immediately after the beginning of culture, HUVECs were confirmed to bescattered evenly around liver tissues.

From the foregoing, it was revealed that a vascularizedthree-dimensional tissue was autonomously generated by coculturing thethree types of cells, i.e., mouse liver tissue, HUVEC and MSC, underappropriate conditions.

2. Periodical Observation of Vascularized Liver Tissue Transplantation

The vascularized liver tissues generated in Section 1 of Results abovewere transplanted into mice, and morphological changes in tissues weretracked (FIG. 6C). Transplantation into CW mice was performed asdescribed in Section 6 of Methods, and morphological changes weretracked as described in Section 7 of Methods.

In the heads of mice transplanted with vascularized liver tissues, bloodperfusion to all over the transplantation site occurred at day 3post-transplantation (FIG. 6C). Further, when observed with a confocalmicroscope, blood perfusion into the inside of transplanted livertissues was confirmed (FIG. 6D).

It was shown by these results that transplantation of vascularized livertissues induced early resumption of blood flow into the inside oftransplanted liver tissues.

Example 5 Integration of Vascular Networks for Intestinal Tissues[Methods] 1. Isolation of Mouse Intestinal Tissues

C57BL/6-Tg mice (Japan SLC, Inc.) anesthetized with diethyl ether (Wako)were laparotomized after disinfection of the abdomen with 70% ethanol.The inlet of the small intestine was cut off by a length of about 20 cm.The lumen of the small intestine thus cut off was washed with 50 ml ofphysiological saline and then cut lengthwise to expose the mucosa whichwas cut into small sections of about 5 cm. Subsequently, the resultantsmall sections were treated in PBS containing 2 mMEthylenediaminetetraacetic acid (EDTA; Dojinkagaku) and 0.5 mMDithiothreitol (DTT; Sigma Chemical Company) at 37° C. for 20 min. Theresultant supernatant was passed through a 100 μm mesh cell strainer andwashed with PBS three times. Finally, the flow-through was filtered witha 40 μm mesh cell strainer. The cell mass retained on the 40 μm meshcell strainer was recovered with a 0.1% BSA-containing Hanks' buffer.

3. Primary Culture of Mouse Intestinal Tissues

Mouse intestinal tissues were cultured using RPMI1640 (Wako)supplemented with 20% fetal bovine serum (BWT Lot. S-1560), 100 μg/mlpenicillin/streptomycin (Gibco) and Insulin-Transferrin-SeleniumX(Gibco) in a 37° C., 5% CO₂ incubator.

4. Cell Culture

Normal human umbilical vein endothelial cells (HUVECs) (Lonza CC-2517)were cultured using a medium prepared especially for culturing HUVECs[EGM™ BulletKit™ (Lonza CC-4133)] within a guaranteed passage number (5passages). Human mesenchymal stem cells (hMSCs) (Lonza PT-2501) werecultured using a medium prepared especially for culturing hMSCs [MSCGM™BulletKit™ (Lonza PT3001)] within a guaranteed passage number (5passages). Both HUVECs and hMSCs were cultured in a 37° C., 5% CO₂incubator.

5. Preparation of Three-Dimensional Tissues with Vascular Networks

For chronological observation, 20 mouse intestinal tissues were leftstanding in each well of PrimeSurface™ 96-well U plate (SumitomoBakelite) preliminarily filled with a medium for intestinal tissues.Then, 5×10⁴ HUVECs and 5×10³ hMSCs were seeded in each well. The platewas then incubated in a 37° C. incubator for 1 day.

6. Chronological Observation of Cell Coculture with Stereomicroscope

Coculture was performed for tracking chronological changes with astereomicroscope. Briefly, mouse intestinal tissues were left standingin each well of a 24-well plate, and 2×10⁶ HUVECs and 2×10⁵ hMSCs wereseeded in each well. After seeding, the plate was set in astereomicroscope (Leica DFC300FX) and morphological changes caused bycoculture were observed.

7. Experimental Animals

NOD/SCID mice (Sankyo Labo Service Co., Tokyo, Japan) used astransplantation animal were bred under a SPF environment with alight-dark cycle consisting of 10 hours for day and 14 hours for night.The breeding of experimental animals were entrusted to the AnimalExperiment Center, Joint Research Support Section, Advanced MedicalResearch Center, Yokohama City University. Animal experiments wereperformed in accordance with the ethical guidelines stipulated byYokohama City University.

8. Transplantation into CW Mice

The CW mice prepared underwent transplantation after their brainsurfaces were exposed by removing the glass of the cranial window. Thosemice which did not have any sign of bleeding, inflammation or infectionon their brain surfaces were used. After anesthetization, the areasurrounding the cranial window was disinfected with 70% ethanol. Thepointed end of an 18G needle was inserted into the border between thecustom-made circular slide glass and Aron Alpha and so manipulated as topeel off the slide glass without damaging the brain surface. Thus, thebrain surface was exposed. Subsequently, the brain surface was washedwith physiological saline. A transplant was left standing near thecenter of the brain surface, and the custom-made slide glass wasremounted. To ensure no gap would be left, the space between the slideglass and the brain surface was filled with physiological saline and,thereafter, the slide glass was sealed tightly with an adhesive preparedfrom coatley plastic powder and Aron Alpha, in the same manner asperformed at the time of preparation of CW mice.

9. Periodical observation_with Confocal Microscope of the TissuesTransplanted into CW Mice

The three-dimensional tissues transplanted into CW mice in the precedingSection 8 were observed.

Those mice which underwent transplantation were anesthetized byketalar/xylazine mixed anesthesia in the same manner as in Section 11above. Each mouse was fixed on a 25×60 mm micro cover glass (Matsunami)in the supine position so that the cranial window would become level.Morphological changes of the transplanted three-dimensional tissues withvascular networks were observed with a confocal microscope (LEICATCS-SP5).

[Results] 1. Generation of Vascularized Three-Dimensional Tissues byCoculture of Mouse Intestinal Tissues, Vascular Endothelial Cells andMesenchymal Stem Cells

Culture was performed as described in Section 4 of Methods aboveImmediately after the beginning of culture, cells were scattered aroundintestinal tissues, and no three-dimensional tissues visible with eyeswere recognized. At 4 hours of culture, however, interactions betweencells started, and scattered cells began to gather closely. At 8 hoursof culture in an advanced stage, cells so aggregated as to coverintestinal tissues and gradually constituted a three-dimensionalstructure. Finally, at 24 hours of culture, self-organization progressedfurther and a vascularized three-dimensional tissue was constituted(FIG. 7A, 7B). On the other hand, when coculture was not performed butintestinal tissues alone were cultured, neither vascularization norformation of three-dimensional tissues was recognized (FIG. 7B).

Further, by culturing as described in Section 4 of Methods above, anattempt was made to decrease the size of vascularized three-dimensionaltissues in a culture plate (substrate?) of such a shape thatcells/tissues would gather in the bottom (FIG. 7B). When mouseintestinal tissues were cocultured with HUVECs and MSCs,three-dimensional tissues were formed at 24 hours of culture. In orderto track morphological changes in cells, fluorescence-labeled mouseintestinal tissues were cocultured with various kinds of cells (FIG.7B). Briefly, intestinal tissues isolated from mice (FIG. 7B: red),HUVECs into which green fluorescent protein (GFP) had been introduced(FIG. 7B) and MSCs were cocultured, and cell morphology was observedwith a confocal microscope Immediately after the beginning of culture,HUVECs were confirmed to be scattered evenly around intestinal tissues.

From the foregoing, it was revealed that a vascularizedthree-dimensional tissue was autonomously generated by coculturing thethree types of cells, i.e., mouse intestinal tissue, HUVEC and MSC,under appropriate conditions.

2. Periodical Observation of Vascularized Intestinal TissueTransplantation

The vascularized intestinal tissues generated in Section 1 of Resultsabove were transplanted into mice and morphological changes in tissuewere tracked (FIG. 7C). Vascularized intestinal tissues weretransplanted into cranial window (CW) mice as described in Section 6 ofMethods, and morphological changes were tracked as described in Section7 of Methods.

In the mouse heads transplanted with vascularized intestinal tissues,blood perfusion to all over the transplantation site occurred at day 3post-transplantation (FIG. 7C). Further, observation with a confocalmicroscope confirmed that blood perfusion into the inside of thetransplanted intestinal tissues occurred at day 3 post-transplantation.(FIG. 7D).

It was shown by these results that transplantation of vascularizedintestinal tissues induced early resumption of blood flow into theinside of the transplanted intestinal tissues.

Example 6 Integration of Vascular Networks for Pulmonary Tissues[Methods] 1. Isolation of Mouse Pulmonary Tissues

C57BL/6-Tg mice (Japan SLC, Inc.) anesthetized with diethyl ether (Wako)were laparotomized after disinfection of the abdomen with 70% ethanol,and the lungs were cut out. The lungs were washed with physiologicalsaline and minced with scissors. The minced lung was filtered with a 100μm mesh cell strainer while adding Hanks' buffer (HBSS, Gibco)containing 0.1% albumin from bovine serum (BSA, Sigma) little by little.The flow-through was filtered with a 40 μm mesh cell strainer. The cellmass retained on the 40 μm mesh cell strainer was recovered with a 0.1%BSA-containing Hanks' buffer.

2. Cell Culture

Normal human umbilical vein endothelial cells (HUVECs) (Lonza CC-2517)were cultured using a medium prepared especially for culturing HUVECs[EGM™ BulletKit™ (Lonza CC-4133)] within a guaranteed passage number (5passages). Human mesenchymal stem cells (hMSCs) (Lonza PT-2501) werecultured using a medium prepared especially for culturing hMSCs [MSCGM™BulletKit™ (Lonza PT3001)] within a guaranteed passage number (5passages). Both HUVECs and hMSCs were cultured in a 37° C., 5% CO₂incubator.

3. Preparation of Three-Dimensional Tissues with Vascular Networks

For chronological observation, 20 mouse pulmonary tissues were leftstanding in each well of PrimeSurface™ 96-well U plate (SumitomoBakelite) filled with a medium for pulmonary tissues. Then, 5×10⁴ HUVECsand 5×10³ hMSCs were seeded in each well. The plate was then incubatedin a 37° C. incubator for 1 day. Further, mouse pulmonary tissues wereleft standing in each well of a 24-well plate. Then, 2×10⁶ HUVECs and2×10⁵ hMSCs were seeded in each well.

4. Chronological Observation of Cell Coculture with Stereomicroscope

Coculture was performed for tracking chronological changes with astereomicroscope. Briefly, 20 mouse pulmonary tissues were left standingin each well of a 24-well plate. HUVECs (2×10⁶ cells) and hMSCs (2×10⁵cells) were seeded in each well. After seeding, the plate was set in astereomicroscope (Leica DFC300FX) and morphological changes caused bycoculture were observed.

5. Experimental Animals

NOD/SCID mice (Sankyo Labo Service Co., Tokyo, Japan) used astransplantation animal were bred under a SPF environment with alight-dark cycle consisting of 10 hours for day and 14 hours for night.The breeding of experimental animals were entrusted to the AnimalExperiment Center, Joint Research Support Section, Advanced MedicalResearch Center, Yokohama City University. Animal experiments wereperformed in accordance with the ethical guidelines stipulated byYokohama City University.

6. Transplantation into CW Mice

The CW mice prepared in Section 8 underwent transplantation after theirbrain surfaces were exposed by removing the glass of the cranial window.Those mice which did not have any sign of bleeding, inflammation orinfection on their brain surfaces were used. After anesthetization, thearea surrounding the cranial window was disinfected with 70% ethanol.The pointed end of an 18G needle was inserted into the border linebetween the custom-made circular slide glass and Aron Alpha and somanipulated as to peel off the slide glass without damaging the brainsurface. Thus, the brain surface was exposed. Subsequently, the brainsurface was washed with physiological saline. A tissue transplant wasleft standing near the center of the brain surface, and the slide glasswas remounted. To ensure no gap would be left, the space between theslide glass and the brain surface was filled with physiological salineand, thereafter, the slide glass was sealed tightly with an adhesiveprepared from coatley plastic powder and Aron Alpha, in the same manneras performed at the time of preparation of CW mouse.

7. Periodical observation with Confocal Microscope of the TissuesTransplanted into CW Mice

The three-dimensional tissues transplanted into CW mice in Section 9were observed.

Those mice which underwent transplantation were anesthetized byketalar/xylazine mixed anesthesia in the same manner as in Section 11above. Each mouse was fixed on a 25×60 mm micro cover glass (Matsunami)in the supine position so that the cranial window would become level.Morphological changes of the transplanted three-dimensional tissues withvascular networks were observed with a confocal microscope (LEICATCS-SP5).

[Results] 1. Generation of Three-Dimensional Tissues by CoculturingMouse Pulmonary Tissues, Vascular Endothelial Cells and Mesenchymal StemCells

Culture was performed as described in Section 6 of Methods above.Immediately after the beginning of culture, cells were scattered aroundpulmonary tissues, and no three-dimensional tissues visible with eyeswere recognized. At 4 hours of culture, however, interactions betweencells started, and scattered cells began to gather closely. At 8 hoursof culture in an advanced stage, cells so aggregated as to coverpulmonary tissues and gradually constituted a three-dimensionalstructure. Finally, at 24 hours of culture, self-organization progressedfurther and a vascularized three-dimensional tissue was constituted(FIG. 8A). On the other hand, when coculture was not performed butpulmonary tissues alone were cultured, neither vascularization norformation of three-dimensional tissues was recognized (FIG. 8A).

Further, by culturing cells as described in Section 4 of Methods above,an attempt was made to decrease the size of vascularizedthree-dimensional tissues in a culture plate (substrate?) of such ashape that cells/tissues would gather in the bottom (FIG. 2). When mousepulmonary tissues were cocultured with HUVEC and MSC, three-dimensionaltissues were formed at 24 hours of culture. In order to trackmorphological changes in cells, coculture experiments were performedusing fluorescence-labeled mouse pulmonary tissues and various kinds ofcells (FIG. 8A). Briefly, pulmonary tissues isolated from mice (FIG. 8A:red), HUVECs into which green fluorescent protein (GFP) had beenintroduced (FIG. 8A: green) and MSC were cocultured, followed byobservation of cell morphology under a confocal microscope. Immediatelyafter the beginning of culture, HUVECs were confirmed to be scatteredevenly around pulmonary tissues.

From the foregoing, it was revealed that a vascularizedthree-dimensional tissue was autonomously generated by coculturing thethree types of cells, i.e., mouse pulmonary tissue, HUVEC and MSC, underappropriate conditions.

2. Periodical Observation of Vascularized Pulmonary TissueTransplantation

The vascularized pulmonary tissues generated in Section 1 of Resultsabove were transplanted into mice, and morphological changes in tissueswere tracked (FIG. 8B). Transplantation into CW mice was performed asdescribed in Section 16 of Methods, and morphological changes weretracked as described in Section 7 of Methods.

In the heads of mice transplanted with vascularized pulmonary tissues,blood perfusion to all over the transplantation site occurred at day 3post-transplantation (FIG. 8B). Further, when observed with a confocalmicroscope, blood perfusion into the inside of transplanted livertissues was confirmed at day 7 post-transplantation (FIG. 8C).

It was shown by these results that transplantation of vascularizedpulmonary tissues induced early resumption of blood flow into the insideof transplanted pulmonary tissues.

Example 7 Integration of Vascular Networks for iPS Cell-DerivedEndodermal Tissues [Methods and Results] 1. Directed Differentiation ofiPS Cells

Expanded but undifferentiated iPS cells (kindly provided by Dr.Nakauchi, Tokyo University; TkDA3 clone; established from dermalfibroblasts) were washed once with a washing medium (DMEM/F12; LifeTechnologies 11320). A cultured cell dissociating solution (FunakoshiAT104) was added to 100 mm dishes in an amount of 1 ml per dish. Cellswere recovered into 50 ml centrifugal tubes and subjected tocentrifugation at 900 rpm for 5 min. After taking a cell count, cellswere seeded on Matrigel™-coated 60 mm dishes at a density of 1.5×10⁶cells per dish. Matrigel™-coating was performed as follows. Briefly, BDMatrigel™ basement membrane matrix (BD Japan 356231) was diluted 30-foldwith DMEM (Life Technologies 1196118). The thus diluted gel was added to60 mm dishes (2 ml/dish), which were left standing at room temperaturefor 2 hr. As a culture broth, an iPS culture medium supplemented withROCK inhibitor Y-27632 (Calbiochem 688000) was used. Cells wereincubated in a 37° C. incubator for 24 hr to induce cell adhesion.Subsequently, the culture broth was exchanged with a directeddifferentiation medium. This medium was RPMI-1640 (Wako Pure Chemicals189-02025) supplemented with B-27™ Supplement Minus Insulin (LifeTechnologies 0050129SA) (1/100 dilution) and 100 ng/μl Activin A(Ajinomoto). While exchanging the medium every 2 days, cells werecultured for 6 days to allow directed differentiation into definitiveendoderms. The degree of differentiation into endodermal lineage wasconfirmed by quantitative PCR and immunostaining.

2. Preparation of iPS Cell-Derived Endodermal Tissues

Human iPS cells which had undergone directed differentiation intodefinitive endoderms were seeded in each well of EZSPHERE™ (Asahi Glass4810-900 6-well-Flat bottom) at a density of 1.0×10⁶ cells/well. As aculture broth, a 1:1 mixture of a medium kit for sole use withhepatocytes (HCM™ BulletKit™; Lonza CC3198) and EGM™ BulletKit™ (LonzaCC-4133) was used. Cells were cultured in a 37° C. incubator for 8 days,with half of the medium exchanged every 2 days, to thereby preparesteric endodermal tissues of 50-500 μm in diameter.

3. Preparation of Three-Dimensional Tissues with Human VasculaturesUsing 96-Well U Plate

One to twenty iPS cell-derived endodermal tissues were left standing ineach well of PrimeSurface™ 96-Well U Plate (Sumitomo Bakelite)preliminarily filled with the medium for culturing iPS cell-derivedendodermal tissues described in Section 2 above. Then, 1.0×10⁴ HUVECsand 1.0×10³ hMSCs were seeded in each well. Subsequently, the cells wereincubated in a 37° C. incubator for 4 days.

As a result, it became clear that endodermal tissues, when coculturedwith human vascular endothelial cells and mesenchymal stem cells,autonomously induced a three-dimensional tissue (FIG. 9B). It was alsofound that in the thus induced tissue, human vascular endothelial cellsformed lumen-like structures to form a vascularized tissue (FIG. 9C).Since the formation of such a three-dimensional tissue was neverconfirmed in the monoculture group of iPS cell-derived endodermaltissues, it was demonstrated that use of the method of the presentinvention is essential for preparing vascularized tissues (FIG. 9B).

All publications, patents and patent applications cited herein areincorporated herein by reference in their entirety.

INDUSTRIAL APPLICABILITY

Biological tissues integrated with a vascular system according to thepresent invention are applicable to generation of human functionalcells, organ transplantation, drug discovery screening, new analyticalsystems for evaluating such factors as the relationship betweendevelopment of drug efficacy and blood vessels.

1. A method of integrating a biological tissue with a vascular system invitro, comprising coculturing a biological tissue with vascular cellsand mesenchymal cells.
 2. The method of claim 1, wherein the biologicaltissue is cocultured with vascular cells and mesenchymal cells withoutusing scaffold materials.
 3. The method of claim 1 or 2, wherein bycoculturing the biological tissue with vascular cells and mesenchymalcells, the biological tissue is integrated with a vascular system sothat the function of the biological tissue is maintained and/orimproved.
 4. A biological tissue which has been integrated with avascular system by the method of claim
 1. 5. A method of preparing atissue or an organ, comprising transplanting the biological tissue ofclaim 4 into a non-human animal and differentiating the biologicaltissue into a tissue or an organ in which vascular networks have beenconstructed.
 6. A method of regeneration or function recovery of atissue or an organ, comprising transplanting the biological tissue ofclaim 4 into a human or a non-human animal and differentiating thebiological tissue into a tissue or an organ in which vascular networkshave been constructed.
 7. A method of preparing a non-human chimericanimal, comprising transplanting the biological tissue of claim 4 into anon-human animal and differentiating the biological tissue into a tissueor organ in which vascular networks have been constructed.
 8. A methodof evaluating a drug, comprising using at least one member selected fromthe group consisting of the biological tissue of claim 4, the tissue ororgan prepared by the method of claim 5, and the non-human chimericanimal prepared by the method of claim
 7. 9. A composition forregenerative medicine, comprising the biological tissue of claim
 4. 10.The composition of claim 9, which is used for preparing a tissue or anorgan.
 11. The composition of claim 9, which is used for regeneration orfunction recovery of a tissue or an organ.
 12. The composition of anyone of claims 9 to 11, wherein the biological tissue differentiates intoa tissue or an organ with vascular networks upon transplantation into aliving body.